6533b851fe1ef96bd12a8c41

RESEARCH PRODUCT

Small Nitrogenous Compounds

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description

Because of the constant turnover of proteins, protein-bound and free amino acids exist in a dynamic equilibrium. The intracellular pool of free amino acids, which is replenished by the hydrolysis of existing proteins, by uptake from the intercellular space and by de novo synthesis, is available for protein synthesis and for the many other metabolic processes dependent upon amino acids. The concentration of free amino acids is always lower than that of the protein-bound residues, one limiting factor being the strong osmotic effects of such low molecular weight compounds. Thus, there is no specific amino acid store in an organism; it is more the case that enzymes and structural proteins themselves represent the reserve of amino acids. Insect larvae, which require large amounts of amino acids for metamorphosis and sclerotization of the cuticula, make use of extracellular proteins as a source of amino acids; examples include the larval haemolymph proteins of some dipterans (p. 191) and possibly the haemoglobins of the non-biting midges (Chironomidae) (p. 273).