Interaction of L-alanosine (NSC 153, 353) with enzymes metabolizing L-aspartic acid, L-glutamic acid and their amides

Abstract

A comprehensive analysis has been made of the manner in which L-alanosine [ L-2-amino-3-(N-nitroso, N-hydroxy) aminopropionic acid] interacts with the enzymes responsible for the metabolism of the dicarboxylic amino acids and their amides. The drug impedes the transport of L-aspartic acid and, to a lesser degree, of L-glutamic acid, L-asparagine and L-glutamine by lymphoblasts. in vitro; in each of these instances, inhibition is apparently competitive in type. Of the enzymes involved in the metabolism of L-aspartic acid, adenylosuccinate synthetase (EC 6.3.4.4). SAICAR synthetase (5-amino-4-imidazole-N-succinocarboxamide ribonucleotide synthetase) (EC 6.3.2.6). L-aspartyl tRNA synthetase (EC 6.1.1.12), L-aspartate transcarbamylase (EC 2.1.3.2) and L-aspartate aminotransferase (EC 2.6.1.1) were inhibited by L-alanosine; moreover, each of these enzymes except L-aspartyl tRNA synthetase accepted the antibiotic as substrate, although at substantially diminished rates. Of the enzymes involved in the metabolism of L-glutamic acid, L-alanosine inhibited only L-glutamine synthetase (EC 6.3.1.2) and L-glutamate decarboxylase (EC 4.1.1.15) to a prominent degree; this last enzyme was also capable of decarboxylating L-alanosine. Of the enzymes metabolizing L-asparagine and/or L-glutamine. only the L-glutaminase activity of L-asparagine amidohydrolase (EC 3.5.1.1) (with L-glutamine as substrate) and, to a lesser degree, carbamyl phosphate synthetase II (EC 2.7.2.9) were inhibited by the antibiotic. Although L-alanosine provokes a rise in the concentration of inosinic acid (IMP) in vitro, pointing to the conclusion that the drug is capable of inhibiting adenylosuccinate synthetase under these circumstances, no such rise was seen in vivo either in tumor or liver. However, 1 and 5 hr after administration L-alanosine depressed hepatic ATP and NAD pools, an effect which indicates that the drug is. in fact, restricting the intracellular concentration of adenine nucleotides. Of the metabolites of L-alanosine formed in vitro, α-decarboxy alanosine, α-keto alanosine, α-hydroxy alanosine. alanosyl IMP and N-carbamyl L-alanosine did not inhibit adenylosuccinate synthetase to any prominent degree, whereas the metabolite generated by SAICAR synthetase powerfully inhibited this enzyme, with a K_i, of 0.3μM. Parenteral therapeutic doses of L-alanosine produced striking increases in the concentrations of L-aspartic acid in tumor and liver as well as of L-aspartic and L-glutamic acids in urine. It is concluded that the N-hydioxy, N-nitroso functionality of L-alanosine is analogous in structure to the β-carboxyls of L-aspartic and L-glutamic acids, respectively; this analogy permits L-alanosine to be anabolized and catabolized via several of the enzymatic routes which ordinarily operate on these dicarboxylic amino acids.