Chemical stability and metabolic utilization of asparagine peptides

Abstract

l-Leucyl- l-asparagine and l-asparaginyl- l-leucine are utilized as well as l-asparaginylglycine and glycyl- l-asparagine by Leuc. mesenteroides. The growth response to these peptides approximates that to l-aspartic acid and is far superior to that to l-asparagine. l-Aspartylglycine and glycyl- l-aspartic acid at high concentrations are superior to l-aspartic acid as a source of the dicarboxylic acid. The glycine peptides serve as better sources of glycine than glycine itself. The growth response to the leucine peptides is equal to that to leucine. Cell-free extracts of Leuc. mesenteroides show strong asparaginase activity. Observations on the enzymatic splitting of the asparagine peptides suggest that the peptides are cleaved into the amide and glycine or leucine and that the free amide is deamidated. It appears that the superior utilization of asparagine peptides when compared with that of asparagine is the result of the inability of the latter to reach the sites of its metabolism by the bacterial cell. Procedures for the syntheses of leucylasparagine, asparaginylleucine, α-aspartylglycine and glycylaspartic acid are described. The instability of glycylasparagine in acid and of asparaginylglycine in alkali is demonstrated and discussed.