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

Abstract

SUMMARYSynthesis 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 ( 1 0 -8~) restored synthesis of the enzyme to a level greater than the maximum recorded in biotin-optimal yeast. Homobiotin ( 1 0 4~) had a similar though less marked effect.

A specific requirement for biotin in the synthesis of ornithine carbamoyltransferase by yeast

“…Dixon & Rose (1964) reported that growth and OCT synthesis were markedly restricted in yeast grown in biotin-deficient medium as compared with yeast grown in biotin-optimum medium. They also showed that the biotin homologues norbiotin and homobiotin caused a very marked stimulation in OCT synthesis in yeast grown in biotin-deficient medium without affecting growth; these homologues had no detectable effect on OCT synthesis in yeast grown in a medium containing an optimum concentration of biotin.…”

“…This difference in the effect of aspartate on OCT synthesis in these two organisms prompted a further examination ofthe role ofbiotin in OCT synthesis by the yeast. During this work, it was found that the biotin homologues norbiotin and homobiotin caused a marked stimulation of OCT synthesis in biotin-deficient yeast without affecting growth (Dixon & Rose, 1964). The present paper describes further experiments on the requirement for biotin in OCT synthesis by the yeast, particularly with regard to the effect of norbiotin, and reports evidence for a very specific role for biotin in the synthesis of this enzyme.…”

“…The yeast used was a biotin-requiring strain of Saccharomyces cerevisiae Fleischmann (Rose, 1960), obtained from Miss M. T. Clement of the Division of Biosciences, National Research Council of Canada, Ottawa, Canada. It was maintained and stored as described by Dixon & Rose (1964). * Abbreviation: OCT, ornithine carbamoyltransferase.…”

“…The present paper describes further experiments on the requirement for biotin in OCT synthesis by the yeast, particularly with regard to the effect of norbiotin, and reports evidence for a very specific role for biotin in the synthesis of this enzyme. A preliminary account of some of these experiments has been published (Dixon & Rose, 1965).…”

Biotin and the Metabolism of Baker's Yeast

“…The increased pyruvate pool in biolin-deficicnt yeast leads to the formation of ethanol, and the amounts of the amino acids derived from pyruvate are either increased (alanine and valine) or un affected (leucinc) by biotin-deficiency (Table I). 10 The limited amount of oxaloacetate formed under biotinreslricted growth is driven more strongly in the direction of the TCA cycle and the formation of glutamatc than in the direction of aspartate synthesis. This is suggested by behaviour of the arginine-citrulline-systcm and the rather large gluta mate pool in biotin-deficient yeast (Table I) This phenomenon has also been noticed with some bac teria" where biotin auxotrophic Escherichia coli cells contain more fatty acids after growth in a biotin-deficient than in a biotin-rich medium.…”