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 -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 -ornithine to biotin-deficient medium increased synthesis of the enzyme to a value approximately half of the maximum recorded in biotin-optimal yeast, but -citrulline, -glutamate, -proline, oleate, or cytosine and uracil and their nucleosides and nucleotides had little or no stimulatory effect on synthesis of the enzyme. -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 -aspartate. With yeast grown in unsupplemented biotin-deficient medium, but not in this medium supplemented with aspartate + ornithine, norbiotin (10 ) restored synthesis of the enzyme to a level greater than the maximum recorded in biotin-optimal yeast. Homobiotin (10 ) had a similar though less marked effect.


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