Approaching the Structures of Mammalian Propylamine Transferases and their Genes
Propylamine transferases, spermidine synthase (EC 18.104.22.168) and spermine synthase (EC 22.214.171.124) catalyze the two final, irreversible steps in the conversion of arginine and methionine to spermidine and spermine, respectively. Both of the amino acid precursors are nutritionally essential for animals and are present in animal tissues at low, well-conserved concentrations. Arginine plays a central role in protein catabolism by being an essential intermediate in the conversion of toxic ammonia to excretable nontoxic urea. Methionine, on the other hand, is vitally important for protein synthesis by being the amino acid needed for peptide chain initiation and for the transmethylation reactions involved in the control of metabolism at several steps of transcriptional, translational and post-translational level. The fraction of the precursor amino acids consumed in polyamine synthesis varies a great deal depending on the cell type, the stage of differentiation and the proliferation rate. As to methionine consumption, the share of polyamine synthesis is less than 1% in rat liver (Eloranta and Kajander, 1984) but may exceed 20% in some cultured cells (Iizasa and Carson, 1985). Although detailed action mechanisms of polyamines in animal physiology are poorly known, their essentiality for cellular functions have been widely demonstrated (for references see Tabor and Tabor, 1984; Pegg, 1986).
KeywordsTryptic Peptide Bovine Brain Bacterial Enzyme COLI Bovine Polyamine Synthesis
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