P/CAF-mediated spermidine acetylation regulates histone acetyltransferase activity

Histones and polyamines are important determinants of the chromatin structure. Histones form the core of nucleosome particles and their modification by acetylation of N-terminal tails is involved in chromatin structural changes and transcriptional regulation. Polyamines, including spermidine, are also targets of both cytoplasmic and nuclear acetylation, which in turn alters their affinity for DNA and nucleosomes. Previous studies report the interplay between polyamines metabolism and levels of histone acetylation, but the molecular basis of this effect is still unclear. In this work, we have analyzed the in vitro effect of spermidine on histone H3 acetylation catalyzed by P/CAF, a highly co…

Alzheimer's disease: amino acid levels and brain metabolic status.

Abstract To study brain free amino acids and their relation with dementia we measured, by high-performance liquid chromatography (HPLC), the concentration of eight free amino acids, amines and related compounds. We used temporal cortex (TC) samples obtained from 13 Alzheimer’s disease (AD) patients and an equal number of agematched controls (AC). The patterns of free amino acids, amines and related compounds showed significant quantitative changes in AD conditions with respect to healthy ones. In Alzheimer patients, lower levels of GABA were found in the TC (-57 %). Amino acids glutamate (Glu), and aspartate (Asp) concentrations, also appeared significantly reduced in the TC of AD patients …

Nucleoside phosphotransferase of chick embryo

This paper describes a purification procedure and some properties of a nonspecific nucleoside phosphotransferase of chick embryo, an activity which catalyzes the transfer of chick embryo, an activity which catalyzes the transfer of the phosphate ester from a deoxyribonucleotide or a pyrimidine ribonucleotide to a deoxyribonucleoside acceptor. The enzyme is very unstable to heat, dilution and dialysis and it is almost entirely inactivated by DEAE-cellulose chromatography or gel filtration. A marked enhancement in its stability is caused by numerous nucleotides. In these experiments at least 920-fold purification was obtained by using dTTP (50 microM) as nucleotide protector. The enzyme, puri…

Xanthine oxidase catalyzes the oxidation of retinol.

In mammals, xanthine oxidase (E.C. 1.17.3.2) catalyzes the hydroxylation of a wide variety of heterocyclic substrates such as purines, pyrimidines, and pterins, in addition to aldehydes [1] as all-trans-retinaldehyde [2-5]. Here, we show that buttermilk xanthine oxidase was capable to oxidizing all-trans-retinol (t-ROL) to all-trans-retinaldehyde (t-RAL) that was successively oxidized to all-trans-retinoic acid (t-RA). A rise in the enzyme activity, when t-ROL-CRBP complex was assayed, with respect to the free t-ROL, was observed. Furthermore, treatment of the enzyme with Na2S and glutathione resulted in a significant increment in catalytic activity toward t-ROL and t-RAL, due to the recons…

Sildenafil inhibits the ROS production by xanthine oxidase

Xanthine oxidase (XO) catalyzes the hydroxylation of a wide variety of substrates, including purines, pirimidines, pterins d aldehydes, to acids1. At relatively high oxygen pressure, it generates reactive oxygen species (ROS) as superoxides and hydroxyl radicals. The XO, detected in endothelial and epithelial cell outer surface, has been involved in ischemia/reperfusion injury1,2. Furthermore, XO-ROS production has been implicated in chronic hearth failure, inflammatory diseases, LDL oxidation, atherosclerosis, hypertension, cancer, aging1. Allopurinol, a hypoxanthine analogue developed as xanthine oxidase inhibitor 30 years ago, and oxypurinol, its oxidation product, have proved to be effe…

Proposed reaction mechanism of xanthine dehydrogenase in the oxidation of retinol to retinoic acid in mammary epithelial cells

Inhibition of DNA synthesis in chick embryo retinas, in vitro, by a factor from fetal bovine serum

Fetal bovine serum inhibited deoxyribonucleic acid (DNA) synthesis in chick embryo retina explants. The inhibitory activity was precipitated from fetal bovine serum by 45% saturated ammonium sulfate and isolated by means of Sephadex G-100 and Bio-Gel P-60 columns as a peak with an apparent molecular weight of 7000 Da. DNA-inhibiting activity was heat- and acid-stable and was destroyed by dithiothreitol and alkaline treatment. The purified factor inhibited similarly both DNA synthesis and thymidine kinase activity; 50% inhibitory effect was found with 160 ng, 17 h after the addition into the incubation medium.

Rapid and simultaneous high-performance liquid chromatography assay of polyamines and monoacetylpolyamines in biological specimens

A rapid, resolutive and reproducible reversed-phase high-performance liquid chromatography (RP-HPLC) method was developed for polyamines and acetylpolyamines by adopting pre-column derivatization with benzoyl chloride. In a single run lasting less than 15 min ten polyamines were separated as well as traces of benzoic acid, methylbenzoate and benzoic anhydride. These contaminants, produced during the derivatization reaction, were almost all eliminated by washing steps envisaged in the same procedure. This simple and sensitive method can be applied to routine determination of polyamines in biological samples. A fine application of this procedure to the determination of endogenous content of p…

Implementation of quality system in the biomedical laboratories

SCOPE To study and to diffuse the better strategies for the planning and the validation of inner methods that assure the significance of the analytical data INTRODUCTION Today the ISO/IEC 17025 and the ISO 15189 are sure the better methodologies and internationally recognized in order to assure in the biomedical laboratories the appropriatness of the methods and the quality of the analytical data The ISO/IEC 17025 standard specifies the general requirements a laboratory has to met if it is to be recognized as competent to carry out tests and/or calibrations, including sampling. METHODOLOGY AND RESULTS The planning of an inner method can be constituted from following is made: Recognition of …

Morphological and biochemical effects of glucocorticoids in chick embryo hepatocytes during development

Abstract The administration in ovo of hydrocortisone-21-phosphate caused, in chick embryo liver, a reduction of the number of hepatocytes which can be isolated from 1 mg dry weight of liver and a marked increase of their size. Moreover, the treatment diminished the incorporation of thymidine into acid-insoluble fraction in these cells whilst it augmented the content of protein, RNA, DNA and the level of thymidine kinase/cell. These effects were highest at 8–10 days, then declined with the age, disappearing after 18th day of incubation. Similar effects were obtained by injecting other glucocorticoids or ACTH. Combined treatment with metopirone abolished the effects found with ACTH, but did n…

Low levels of xanthine dehydrogenase and cellular retinol binding protein in tumor mammary epithelial cells are responsible of the retinoic acid deficit

Sildenafil protects human mammary epithelial cells against ROS production induced by estradiol

Several studies suggest that xanthine dehydrogenase (XDH) and its oxidase form (XO) play an important role in various types of ischemic and vascular injuries. Recently, we have demonstrated that estradiol (E2) induces a significant decrease of the expression and activity of XDH and of its conversion to XO in human mammary epithelial cells. E2 is known to induce upregulation of eNOS gene expression in aortic endothelial cells. Because the XO-derived O2·- combines with ·NO to yield ONOO-, and considering that ONOO- converts XDH to XO, the resulting increase of XO activity and reactive oxygen species production would eventually lead to a further increase of ONOO- production, thus creating a vi…

A simple HPLC assay for polyamines and their monoacetylderivatives

Estradiol decreases xanthine dehydrogenase enzyme activity and protein expression innon-tumorigenicand malignant human mammary epithelial cells

The retinoic acid deficiency in breast tumour epithelial cells has been ascribed to an insufficient expression of either the enzyme(s) involved in its biosynthesis or the cellular retinol binding protein (CRBP) or both. In an attempt to define the mechanisms underpinning retinoic acid deficiency in these cell model systems, we have investigated the potential regulatory effect of oestrogen (17β-estradiol) on one key player in retinoic acid biosynthesis, the xanthine dehydrogenase (XDH). This enzyme is consistently expressed and very active in non-malignant human mammary epithelial cells (HMEC), as opposed to tumour MDA-MB231 and MCF7 cells. In these latter two cell lines, as opposed to HMEC …

Regulation of PCAF Activity by Spermidine

Histones and polyamines are important determinants of chromatin structure. Histones are the core of nucleosome particles and their modification by acetylation of N-terminal tails is involved in chromatin structural changes and transcriptional modulation. Polyamines also, including spermidine, are targets of both nuclear and cytoplasmic acetylation, which in turn alters their affinity for DNA and nucleosomes. Previous studies report an interplay existing between polyamines metabolism and levels, and histone acetylation. The relationship between polyamines and histone epigenetics in vivo has been considered in various models of ageing through epigenetic modifications, induction of autophagy a…

Some kinetic properties of the chick embryos nucleoside phosphotransferase

Retinol oxidation to retinoic acid in human thyroid glandular cells.

Abstract Retinoic acid is regarded as the retinol metabolite that controls proliferation and differentiation of epithelial cells. In the present study, we investigated the potential role of xanthine dehydrogenase (XDH) in retinoic acid biosynthesis in human thyroid glandular cells (HTGC). In particular, we observed that cellular retinoids binding proteins (CRBPs) are also implicated in the biosynthetic pathway leading to retinoic acid formation in primary cultures of HTGC, as we have already reported for human mammary epithelial cells (HMEC). After partial protein purification, the enzyme responsible for retinoic acid biosynthesis was identified and quantified as XDH by immunoassay, by its …

Development and validation of a fast and sensitive chromatographic assay for all-trans-retinol and tocopherols in human serum/plasma using liquid-liquid extraction.

A sensitive HPLC assay for all-trans-retinol, a-tocopherol, and g-tocopherols in human serum and plasma is reported. Sample preparation is performed in one step and involves precipitation of proteins and extraction of lipids with two volumes of an ethanol–chloroform mixture (3:1, v/v) without I.S. addition. After removal of the precipitated protein, 20 ml aliquots of the supernatant (equivalent to 6.7 ml of serum or plasma) were injected into the HPLC system and analyzed using fluorometric detection. RP-HPLC was performed using a C18 S3 ODS2 column with a methanol–water step gradient (97:3 to 100) at 1.0 ml/min. The quantification limit expressed as nanograms of analyte per milliliter of se…

Polyamines and ripening of photoreceptor outer segments in chicken embryos.

Abstract Polyamines and their related monoacetyl derivatives were studied in rod outer segment (ROS) and cone outer segment (COS) of photoreceptor cells from chick embryo retina during eye development (7th–18th days). Putrescine was found to be necessary, in the second phase of retinogenesis, to sustain both ROS and COS differentiation and, after acetylation, γ-aminobutyric acid synthesis. On the other hand, spermidine and even more spermine intervene in the third phase of development when photoreceptors mature. Moreover, the presence of N1-acetylspermidine already at the 7th day indicates that in the outer segment of photoreceptor cells too, as in the whole retina, putrescine synthesis com…

Micellar electrokinetic capillary chromatography of polyamines and monoacetylpolyamines.

A selective procedure for qualitative and quantitative analysis of ten polyamines by micellar electrokinetic chromatography (MEKC) was developed. Benzoylated polyamines and acetylpolyamines in micellar phase of SDS (10 mM) were separated at 258C by 20 mM borate buffer pH 8.5, containing 8% ethanol, with an applied voltage of 25 kV (5 mA) and then detected at 198 nm. The experimental factors and operational parameters were optimized by performing analysis at different surfactant concentrations, pH, voltage and temperature with and without ethanol. The repeatibility of migration times and peak heights is a peculiarity of the method here described.

DNA content and thymidine incorporation during chick embryo retina development:hydrocortisone effect

PCAF catalyzes tha acetylation of spermidine to N8-acetylspermidine and regulates its acetylating activity on histones

Post-transcriptional histone acetylation is a well known process playing a crucial role in chromatin assembly and transcription. Here, we report that PCAF, a highly conserved histone acetyltransferase (HAT), can efficiently catalyze acetylation of spermidine to N8-acetylspermidine, at low concentration. Remarkably, we found that spermidine at higher concentration can also inhibit PCAF HAT activity directed against histone H3 in vitro, confirming the in vivo data referred by Eisenberg et al. on the spermidine induced inhibition of H3 acetylation. Surprisingly when we performed HAT assay experiments at low spermidine concentration we observed an activating effect on PCAF on H3 acetylation. Ou…

Ornithine decarboxylase activity during chick embryo retina development:hydrocortisone effect

Micellar electrokinetic chromatography of polyamines and monoacetylpolyamines

A selective procedure for qualitative and quantitative analysis of ten polyamines by micellar electrokinetic chromatography (MEKC) was developed. Benzoylated polyamines and acetylpolyamines in micellar phase of SDS (10 mM) were separated at 25 degrees C by 20 mM borate buffer pH 8.5, containing 8% ethanol, with an applied voltage of 25 kV (5 microA) and then detected at 198 nm. The experimental factors and operational parameters were optimized by performing analysis at different surfactant concentrations, pH, voltage and temperature with and without ethanol. The repeatibility of migration times and peak heights is a peculiarity of the method here described.

Uridine enhances the cytotoxic effect of D-glucosamine in rat C6 glioma cells.

This paper studies the influence of uridine on the effects exerted by D-glucosamine in rat C6 glioma cells. 2 mM uridine increased markedly both the cytotoxic effect of the aminosugar and the inhibition of thymidine incorporation into acid-insoluble fraction. Furthermore the complete resumption of the capacity to incorporate either 3H-thymidine or 3H-mannose which was observed after the removal of the aminosugar, was impeded when the cells were treated contemporaneously with D-glucosamine and uridine. An exposure for 4 hr to 20 mM glucosamine alone enhanced about 15-fold the cellular pool of UDP-N-acetylhexosamines; the addition of 2 mM uridine intensified the expansion of this pool, which …

Development of nucleoside phosphotransferase activity in the cerebral hemispheres of embryonal and adult chick.

In the cerebral hemispheres of the chick embryo, the level of nucleoside phosphotransferase activity is much higher than that of thymidine kinase and it increases progressively during development up to the adult stage. Therefore nucleoside phosphotransferase is not coupled with DNA synthesis.

Partial purification and some properties of a nucleoside phosphotransferase of chick embryos.

A nucleoside phosphotransferase purified about 40fold from chick embryos utilizes efficiently as phosphate donors deoxyribonucleoside and pyrimidine ribonucleoside monophosphates, whereas the pyrimidine deoxyribonucleoside appear to be the preferred acceptors of phosphate. The enzyme is very unstable to heat, dilution and dialysis. A marked enhancement in the stability is caused by nucleotides and it seems associated with the formation of an aggregated state of the protein.

Polyamines and ripening of photoreceptor outer-segment in chicken embryo.

Polyamines and their related monoacetyl derivatives were studied in rod outer segment (ROS) and cone outer segment (COS) of photoreceptor cells from chick embryo retina during eye development (7th-18th days). Putrescine was found to be necessary, in the second phase of retinogenesis, to sustain both ROS and COS differentiation and, after acetylation, gamma-aminobutyric acid synthesis. On the Other hand, spermidine and even more spermine intervene in the third phase of development when photoreceptors mature. Moreover, the presence of Nl-acetylspermidine already at the 7th day indicates that in the outer segment of photoreceptor cells too, as in the whole retina, putrescine synthesis comes ab…

IMPLEMENTATION OF QUALITY SYSTEMS IN THE BIOMEDICAL LABORATORIES

Kinetic properties of a nucleoside phosphotransferase of chick embryo

1. A nonspecific nucleoside phosphotransferase (nucleotide : 3'-deoxynucleotide 5'-phosphotransferase, EC 2.7.1.77), purified from chick embryos, catalyzes the transfer of phosphate ester from a nucleotide donor to a nucleoside acceptor. 2. The enzyme exhibits sigmoidal kinetics with respect to nucleoside monophosphate donors, but with respect to nucleoside di- or triphosphate donors and nucleoside acceptors hyperbolic kinetics were obtained. 3. The nucleoside phosphotransferase of chick embryo is unstable to heat and is protected from inactivation by a large number of nucleosides. 4. Nucleoside di- and triphosphates lower both the concentration of nucleoside monophosphates required for hal…

Xanthine dehydrogenase processes retinol to retinoic acid in human thyroid epitelial cells

Growth-inhibitory response elicited by hydrocortisone in chick embryo hepatocytes

The pattern of polyamine and GABA in chicken embryo retina photoreceptor membranes

Low levels of both xanthine dehydrogenase and of cellular retinol binding protein are responsible for retinoic acid deficiency in malignant human mammary epithelial cells

The seeming impairment of retinoid metabolism in human breast tumor cells has been attributed to the lower expression of cellular retinol binding proteins (CRBPs), of alcohol/retinol dehydrogenases, or aldehyde/retinaldehyde dehydrogenases. In a previous study we indicated that xanthine dehydrogenase (XDH) is able to oxidize actively both all-trans-retinol (t-ROL) bound to the CRBP (holo-CRBP) and all-trans-retinaldehyde (t-RAL) to all-trans-retinoic acid (t-RA) in human mammary epithelial cells (HMEC). Since both XDH and CRBP are required for the biosynthesis of t-RA, we have inspected their bioavailability in both estrogen-responsive and nonresponsive human mammary epithelial cancer cells…

Xanthine dehydrogenase processes retinol to retinoic acid in human mammary epithelial cells

Retinoic acid is considered to be the active metabolite of retinol, able to control differentiation and proliferation of epithelia. Retinoic acid biosynthesis has been widely described with the implication of multiple enzymatic activities. However, our understanding of the cell biological function and regulation of this process is limited. In a recent study we evidenced that milk xanthine oxidase (E.C. 1.17.3.2.) is capable to oxidize all-trans-retinol bound to CRBP (holo-CRBP) to all-trans-retinaldehyde and then to all-trans-retinoic acid. To get further knowledge regarding this process we have evaluated the biosynthetic pathway of retinoic acid in a human mammary epithelial cell line (HME…

The tumor breast cells MCF-7 can synthesize retinoic acid startinf from retinaldehyde

Sildenafil protects epithelial cell through the inhibition of xanthine oxidase and the impairment of ROS production

Recent reports suggest that xanthine oxidase (XO), a modified form of the native xanthine dehydrogenase enzyme, plays an important role in various forms of ischemic and vascular injuries, inflammatory diseases, and chronic heart failure. The XO inhibitors allopurinol and its oxidation product oxypurinol held considerable promises in the treatment of these conditions both in experimental animals and in human clinical trials. More recently, an endothelium-based protective effect of sildenafil, a well-known type-5 phosphodiesterase inhibitor, has been reported in preconditioning prior to ischemia/reperfusion in healthy human subjects. Based on the structural similarities between allopurinol an…

The acetylation of spermidine catalyzed by P/CAF regulates its acetyltransferase activity versus histones

Transcriptional regulation in eukaryotes occurs within a chromatin setting and is strongly inhibited by nucleosomal barriers imposed by histone proteins. Among the well-known covalent modifications of chromatin, the reversible acetylation of specific lysine residues of histones, catalyzed by several acetyltransferase and deacetylases, has been linked to many biological processes including transcriptional regulation. Indeed, many transcriptional coactivators possess histone acetyltransferase (HAT) activity (1). Functional interactions between HAT and polyamines have been previously reported. In particular, it has been shown that polyamines facilitate oligomerization of nucleosomal arrays in …

Inhibitory effect of hydrocortisone administered in ovo on thymidine kinase in chick embryo retina during development

hydrocortisone

Interactions between polyamines, acetylpolyamines and PCAF during histone acetylation.

Polyamines are involved in several gene regulatory functions, as the transcription process. In order to clarify their effect, in an initial “in vitro” biochemical study, we considered their influence on the nuclear PCAF acetyltransferase (PCAF-HAT). In a model system, using both commercial histones and laboratory histone preparations from mammary epithelial cells, we evidenced the inhibitory effect played by 40-180 uM spermidine (Spd) versus PCAF, assayed on 250 nM histone and 40 uM acetyl-CoA. At the same concentrations N8-acetylspermidine (N8-Ac.Spd), the acetylated form of spermidine located in the nucleus, exerts a significant activating effect on the PCAF-HAT. In addition, N8-Ac.Spd se…

Pattern of polyamines and related monoacetyl-derivatives in chick embryo retina during development

Simple high-performance liquid chromatographic assay for polyamines and their monoacetyl derivatives.

A rapid reversed-phase high-performance liquid chromatographic method, using pre-column derivatization with benzoyl chloride and ultraviolet detection at 254 nm, was developed for the simultaneous measurement of polyamines and their monoacetyl derivatives. Calibration curves were linear for concentrations from 1.25 to 25 nmol/ml. The method was employed to assay these compounds in chick embryo retina explants using organic solvent extraction and 1,7-diaminoheptane as an internal standard. This simple and sensitive method can be applied to routine determinations of these compounds in various biological samples.

Biochemical Aspects of Chick Embryo Retina Development: The Effects of Glucocorticoids

In chick embryo retina during development, DNA synthesis and the activities of DNA polymerase, thymidine kinase, thymidylate synthetase, and ornithine decarboxylase (ODC) declined in parallel from day 7 to 12. The administration in ovo of hydrocortisone reduced significantly, particularly at 8-10 days of incubation, both DNA synthesis and the four enzyme activities tested. The effect was dose dependent, reaching the maximum with 50-100 nmol of hydrocortisone, 8-16 h after treatment. The highest inhibition was found for ODC activity (70%), followed by thymidine kinase activity (62%) and DNA synthesis (45%), whereas activities of DNA polymerase and thymidylate synthetase were reduced only by …

Estrogen Inhibits Retinoic Acid Biosynthesis In Tumor Breast Epithelial Cell Lines

Effects of hydrocortisone on chick embryo liver during development

Identification of Insulin in Chick Embryo Retina During Development and Its Inhibitory Effect on DNA Synthesis

Incubation of chick embryo retinal explants with insulin resulted in a pronounced inhibition of thymidine uptake and incorporation into trichloroacetic acid-insoluble fraction. The inhibitory effect was highest with explants from embryos at day 7 and day 8, and thereafter it declined markedly with the age of embryos until day 11. A time-course study of the effect revealed that the inhibition occurred after a lag time; both thymidine uptake and incorporation were not altered significantly after 2-6 h of incubation with insulin, but began to decrease thereafter, reaching the maximum after 16 h. The effect was also dose dependent. After 16 h of incubation, the maximal inhibition (65%) was foun…

Protective Effect of Sildenafil against Estradiol-induced ROS production

Several reports suggest that xanthine dehydrogenase (XDH) and its oxidase form (XO) play an important role in various forms of ischemic and vascular injuries. Recently we have demonstrated that 17β-estradiol (E2) induces a significant decrease of the expression and activity of XDH and its conversion to XO in human mammary epithelial cells. E2 is known to induce upregulation of eNOS gene expression in aortic endothelial cells. In light of the ability of XO-derived O2•¯ to combine with •NO to yield ONOO¯, and considering that ONOO¯ converts XDH to XO, it is important to protect tissues against the XO increased activity and ROS increased production, that would in turn react with •NO to augment…

Influence of hydrocortisone on chick embryo retina development

Treatment of chick embryos in ovo with hydrocortisone-21-phosphate (a single dose of 150 micrograms) caused a marked reduction of retinal thymidine kinase activity 24 h later. The inhibitory effect was highest (65-70%) in 8-10-day-old embryos and declined with age, disappearing after day 15. It was accompanied by a reduction in thickness of the retinal layers. Adrenocorticotropic hormone (ACTH) treatment (10 micrograms daily for 2 days) also produced an age-dependent inhibitory effect on retinal thymidine kinase, whereas treatment with a single dose of 200 micrograms of metopirone, a compound that prevents the 11 beta-hydroxylation of steroid molecules in the adrenal glands, impeded the dec…

Pattern of polyamines and related monoacetyl derivatives in chick embryo retina during development.

Polyamines and related monoacetyl derivatives were studied in chick embryo retina during development (6th-19th day). Putrescine, which is high in the first phase of retinogenesis, is necessary to sustain both tissue proliferation and via N-acetylputrescine, gamma-aminobutyric acid synthesis. A later increase in spermidine and particularly spermine may play a role in the last phase of development when the retina reaches maturation. The presence of N1-acetylspermidine already at the 8th day indicates that in chick embryo retina, putrescine synthesis can depend on two separate pathways. The first involves ornithine decarboxylase activity; the second, spermidine/spermine N1-acetyltransferase an…

Xanthine oxidase catalyzes the synthesis of retinoic acid

Milk xanthine oxidase (xanthine: oxygen oxidoreductase; XO; EC 1.1.3.22) was found to catalyze the conversion of retinaldehyde to retinoic acid. The ability of XO to synthesize all trans-retinoic acid efficiently was assessed by its turnover number of 31.56 min-1, determined at pH 7.0 with 1 nM XO and all trans-retinaldehyde varying between 0.05 to 2 microM. The determination of both retinoid and purine content in milk was also considered in order to correlate their concentrations with kinetic parameters of retinaldehyde oxidase activity. The velocity of the reaction was dependent on the isomeric form of the substrate, the all trans- and 9-cis-forms being the preferred substrates rather tha…

Low levels of both xanthine dehydrogenase and cellular retinol binding protein are responsible of the retinoic acid deficiency in malignant human mammary epithelial cells (abstract)

A factor derived from chick embryo retina which inhibits DNA synthesis of retina itself.

Chick embryo retinas contain a peptide factor that inhibits DNA synthesis in explants of chick embryo retina. The inhibitory factor, obtained by acid/ethanol extraction from 15-day-old chick embryo retinas, was partially purified by affinity chromatography on heparin-sepharose CL-6B and gel filtration on Sephadex G-100. The inhibitor reduced DNA synthesis with maximal effects observed in retinal explants from 7 to 8-day-old chick embryos. The inhibitory effect became apparent after 10 h of incubation and reached the maximum levels after 16 h. DNA-inhibiting activity was heat and acid-stable and was destroyed by trypsin and alkaline treatments. The inhibitory effect was observed in retinal e…