On the Synthesis of Ornithine Carbamoyltransferase in Biotin-deficient Saccharomyces cerevisiae

Abstract

SUMMARY: Synthesis of ornithine carbamoyltransferase by yeast grown in a medium containing a suboptimal concentration of biotin was less than in biotinoptimal yeast and was diminished still further when l-aspartate was included in the biotin-deficient medium, although the presence of this amino acid is known to cause restoration of nucleic acid and total protein synthesis. Addition of l-ornithine to biotin-deficient medium increased synthesis of the enzyme to a value approximately half of the maximum recorded in biotin-optimal yeast, but dl-citrulline, l-glutamate, l-proline, oleate, or cytosine and uracil and their nucleosides and nucleotides had little or no stimulatory effect on synthesis of the enzyme. l-Arginine had little effect on enzyme synthesis by biotin-optimal yeast but caused a marked decrease in synthesis of the enzyme by yeast grown in biotindeficient medium containing l-aspartate. With yeast grown in unsupplemented biotin-deficient medium, but not in this medium supplemented with aspartate + ornithine, norbiotin (10-8 m) restored synthesis of the enzyme to a level greater than the maximum recorded in biotin-optimal yeast. Homobiotin (10-8 m) had a similar though less marked effect.