The synthesis and metabolism of arginine in germinating peas was examined by supplying micromolar quantities of L-citruiline-carbamyl-14C, DL-arginine-carbamyl-14C, and DL-arginine-5-14C to imbibing seeds. Citrulline was readily incorporated into arginine, but the labelled arginine solutions were not extensively metabolized.Extracts of 1-day-old cotyledons were found to catalyze the synthesis of arginine from citrulline in a reaction having absolute requirements for ATP, L-aspartate, and magnesium ions. The extracts were fractionated by (NH4)2SO4 precipitation followed by gel filtration on columns of Sephadex G-50 and G-200. These treatments increased the specific enzyme activity by approximately 36 times. After such treatments the preparations still contained appreciable amounts of argininosuccinate lyase (L-argininosuccinate arginine-lyase, EC 4.3.2.1) activity. The rate of arginine synthesis was altered by increasing the concentrations of L-citrulline, L-aspartate, and ATP. The latter compounds were found to be inhibitory at concentrations of 1 μmole/ml and 4 μmoles/ml, respectively. Arginine synthesis was markedly affected by pH and by additions of arginine and argininosuccinate. It is concluded that germinating pea cotyledons contain appreciable levels of argirrinosuccmate synthetase (L-citrulline:L-aspartate ligase (AMP), EC 6.3.4.5), and furthermore, that this enzyme has importance in arginine biosynthesis during germination.
Coinduction of Nitric Oxide Synthase, Argininosuccinate Synthetase, and Argininosuccinate Lyase in Lipopolysaccharide-treated Rats
