Search results for "ENZYME CATALYSIS"

Computational Modeling of Biological Systems: The LDH Story

2010

Lactate dehydrogenases, LDH, catalyzed reaction has been used in this chapter as a conductor wire to present the evolution and difficulties on computing methods to model chemical reactions in enzymes, since the early calculations based at semiempirical level carried out in gas phase to the recent sophisticated simulations based on hybrid Quantum Mechanical/Molecular Mechanics Dynamics (QM/MM MD) schemes. LDH catalyzes the reversible transformation of pyruvate into lactate. The chemical step consists in a hydride and a proton transfer from the cofactor (NADH) and a protonated histidine (His195), respectively. This fact has generated a lot of controversy about the timing of both transfers in …

2015

Chemical ligation has been used to alter motions in specific regions of dihydrofolate reductase from E. coli and to investigate the effects of localized motional changes on enzyme catalysis. Two isotopic hybrids were prepared; one with the mobile N-terminal segment containing heavy isotopes (2H, 13C, 15N) and the remainder of the protein with natural isotopic abundance, and the other one with only the C-terminal segment isotopically labeled. Kinetic investigations indicated that isotopic substitution of the N-terminal segment affected only a physical step of catalysis, whereas the enzyme chemistry was affected by protein motions from the C-terminal segment. QM/MM studies support the idea th…

Redox Biochemistry of the Genetic Code.

2021

New findings on the chemistry of the amino acids, their role in protein folding, and their sequential primordial introduction have uncovered concealed causalities in genetic code evolution. The genetically encoded amino acids successively provided (i) membrane anchors, (ii) halophilic protein folds, (iii) mesophilic protein folds, (iv) metal ligation, and (v) antioxidation.

Selektive enzymatische Schutzgruppenabspaltungen: Der n-Heptylester als Carboxylschutzgruppe in der Peptidsynthese

1991

Selective Enzymatic Removal of Protecting Groups: n-Heptyl Esters as Carboxy Protecting Functions in Peptide Synthesis Amino acid heptyl (Hep) esters are accessible as generally crystalline hydro tosylates 3 from the amino acids by azeotropic esterification with 1-heptanol in high yields. They can be condensed with Z-, Boc-, and Aloc-protected amino acids to give the dipeptides 7–9 in the presence of 1-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ). From the fully protected dipeptides the N-terminal protecting groups are cleaved by chemical methods without affecting the Hep esters. On the other hand, the heptyl esters can be hydrolyzed under mild conditions (pH = 7.0, 37°C) and with hi…

Stereospecific CC-bond formation with rabbit muscle aldolase - A chemoenzymatic synthesis of (+)-exo-brevicomin

1990

Abstract (+)-(1S,5R,7S)-Exo-brevicomin 9, a sex pheromone of the western pine bark beetle, is synthesized using an aldol reaction catalyzed by fructose-1,6-diphosphate aldolase (EC 4.1.2.13) from rabbit muscle as the key step by which the absolute configuration of the target is established.

Polydimethylsiloxanes with amylose side chains by enzymatic polymerization

1996

Maltoheptaonamide modified polydimethylsiloxane was prepared applying a simplified synthetic pathway in the derivatization sequence of the carbohydrate. The products were characterized by 13C NMR and FT-IR spectroscopy. The glucan side chains of these “sweet siloxanes” were elongated by enzymatic catalysis with potato phosphorylase.

Translocation of enzymes into a mesoporous MOF for enhanced catalytic activity under extreme conditions

2019

Translocation of protease into mesoporous MIL-101-NH2 results in enhanced catalytic activity, excellent recyclability and tolerance to competing enzymes.

Diels-Alderase Catalyzing the Cyclization Step in the Biosynthesis of Spinosyn A

2015

The conversion of putative macrocyclic lactone into the tricyclic compound, as a key step in the biosynthesis of spinosyn A , has been theoretically investigated using DFT methods. The relatively low activation free energy computed for the cyclization process of the actual macrocyclic lactone (21.0 kcal/mol) furnishes a rationalization for a spontaneous ( i.e. nonenzymatically catalyzed) cyclization process in the biosynthesis of spinosyn A . A geometric analysis of putative macrocyclic lactone indicates that a slight strain on the lactone at the active site of the SpnF gene could decrease the activation free energy to ca . 16 kcal/mol. This nonspecific participation of the enzyme, which ac…

Lipase-catalysed preparation of acyl derivatives of the germacranolide sesquiterpenoid cnicin

2009

Several acyl derivatives of cnicin were obtained through lipase-catalysed acylation and alcoholysis reactions. In most reactions lipases showed a regioselective behaviour affording only one product. Longer chain acyl derivatives were prepared at lower temperature than the used in lipase-catalysed reactions, to preclude side products formation. The enzymatic approach let to prepare a family of novel acetyl and fatty acid derivatives of cnicin which are not obtainable following traditional organic synthetic procedures.

Bifunctional Acid-Base Catalysis

2011

Acid-base catalysis with bifunctional catalysts is a very prominent catalytic strategy in both small-molecule organocatalysts as well as enzyme catalysis. In both worlds, small-molecule catalysts and enzymatic catalysis, a variety of different general acids or hydrogen bond donors are used. In this chapter, important parallels between small molecule catalysts and enzymes are discussed, and a comparison is also made to the emerging field of frustrated Lewis pair catalysis.