Regulation of arginine biosynthesis in Chlamydomonas reinhardii: studies in vivo and of ornithine transcarbamoylase and argininosuccinate lyase activities.

Abstract

1. Incorporation of [14C]- carbon dioxide into the arginine residue of the protein fraction was used as a measurement of the rate of arginine biosynthesis by the intact cells of Chlamydomonas reinhardii. The rate of synthesis in the presence of exogenous arginine was less than in its absence; the rate by cells grown in the presence of the amino acid was less than by cells grown in its absence. 2. Activities of ornithine transcarbamoylase and argininosuccinate lyase were the same in extracts from cells grown in the presence of arginine as in those from cells grown in its absence. 3. The activity of ornithine transcarbamoylase decreased when the alga was grown more slowly at lower light intensities. 4. The activities of both ornithine transcarbamoylase and argininosuccinate lyase increased when the wild-type alga was deprived of a nitrogen source and when the arginine auxotroph arg-2 was deprived of arginine.