Protein-disulphide Reductase Activity in Yeast

Abstract

A STRAIN of Saccharomyces cerevisiae which in batch culture demonstrated little tendency to elongate was shown to do so in continuous culture when the supply of nitrogen was limited¹. Because fewer cells elongated when sulphydryl compounds or sodium selenate were added to the medium, the sulphydryl–disulphide balance in the cells seemed to be implicated. Later investigations with the same yeast² revealed that the change in cell shape was not closely paralleled by changes in total and individual carbohydrates, proteins, nucleic acids and lipids of the cells. Attention was therefore directed to enzymes thought to be important in cell extension. Nickerson et al. placed special emphasis on a protein-disulphide reductase system controlling the formation of disulphide bridges in mannan-protein of the wall. They demonstrated in bakers' yeast³ and Candida albicans⁴ that after oxidation with potassium ferricyanide of isolated cell wall protein, the disulphide linkages were reduced by isolated mitochondria. The protein-disulphide-reductase activity was, however, very low in a mutant strain of C. albicans with elongated cells⁴. It was of interest, therefore, to compare activities of mitochondria isolated from elongated and ovoid cells of our strain of bakers' yeast.