LEVELS OF BIOTIN ENZYMES DURING UNBALANCED GROWTH AND DEATH OF BIOTIN-DEFICIENT YEAST CELLS

In order to clarify the mechanism of death of yeast due to biotin-deficiency in the presence of aspartic acid, changes in the activities of two kinds of biotin enzymes, pyruvate carboxylase and acetyl-CoA carboxylase, were examined. From the fact that the extent of decrease of pyruvate carboxylase activity in the cells cultured in the biotin-deficient NH4-medium was about two-fold larger than that of acetyl-CoA carboxylase in the same cells, it could be assumed that these cells were deficient in aspartic acid but not in fatty acids. In addition, when the biotin-deficient cells were transferred to biotin- free NH4-medium supplemented with a fatty acid mixture, the growth was the same as that in the medium without fatty acids.In the biotin-deficient NH4-medium, the growth might be restrained by the reduced activity of pyruvate carboxylase that limits the synthesis of aspartic acid, but when these cells were transferred to the biotin-free Asp-medium they could again begin to grow by producing cell protein and other nitrogenous substances with the supply of aspartic acid. However, during this growth, the lowered activity of acetyl-CoA carboxylase due to biotin deficiency decreased still more gradually, thus resulting in insufficient synthesis of fatty acids. Therefore, it may be that this unbalanced synthesis of cell components, leading especially to impairment of the cell surface structure containing fatty acids, is what makes the cells fall into death.