Arginine catabolism and the arginine succinyltransferase pathway in Escherichia coli

Abstract

Arginine catabolism produces ammonia without transferring nitrogen to another compound, yet the only known pathway of arginine catabolism in Escherichia coli (through arginine decarboxylase) does not produce ammonia. Our aims were to find the ammonia-producing pathway of arginine catabolism in E. coli and to examine its function. We showed that the only previously described pathway of arginine catabolism, which does not produce ammonia, accounted for only 3% of the arginine consumed. A search for another arginine catabolic pathway led to discovery of the ammonia-producing arginine succinyltransferase (AST) pathway in E. coli. Nitrogen limitation induced this pathway in both E. coli and Klebsiella aerogenes, but the mechanisms of activation clearly differed in these two organisms. We identified the E. coli gene for succinylornithine aminotransferase, the third enzyme of the AST pathway, which appears to be the first of an astCADBE operon. Its disruption prevented arginine catabolism, impaired ornithine utilization, and affected the synthesis of all the enzymes of the AST pathway. Disruption of astB eliminated succinylarginine dihydrolase activity and prevented arginine utilization but did not impair ornithine catabolism. Overproduction of AST enzymes resulted in faster growth with arginine and aspartate. We conclude that the AST pathway is necessary for aerobic arginine catabolism in E. coli and that at least one enzyme of this pathway contributes to ornithine catabolism.

FIG. 1

Arginine catabolism by the ADC pathway and the routes of putrescine synthesis.

FIG. 2

AST pathway of arginine catabolism.

FIG. 3

Deduced amino acid sequence of succinylornithine transaminase. The underlined residues correspond to those determined by direct protein sequencing.

FIG. 4

AST enzyme activities in mutants with disruptions in astC and astB. Activity in W3110 (wild type) (black bars), in the astB derivative (white bars), and in the astC derivative (cross-hatched bars) is shown. The values given are the averages from at least five cultures. Activities are given in micromoles of product per hour per milligram of total protein; the error bars show the standard error of the mean. SOT, succinylornithine transaminase; SGSDH, succinylglutamic semialdehyde dehydrogenase; SAD, succinylarginine dihydrolase; SGDS, succinylglutamate desuccinylase.