Abstract
An acid protease inhibitor (S-PI) accelerated the growth of Rhodotorula glutinis. This acceleration of the growth was observed only when the pH of the culture fluid lowered during the cultivation, but was not observed when the pH of the culture fluid was adjusted to 2.8 with NaOH. The increase in number of cells was closely related to cell deaths. The cell deaths were observed in an active growing state but not in a resting state. S-PI increased the DNA, RNA and protein content in the cell and decreased the lipid, especially the phos-pholipid content. When the yeast was cultured in an acidic medium having an initial pH of 1.8 in the presence of S-PI, the decrease of the phospholipid in the cell preceded, followed by the leakage of potassium ion, UV absorbing materials and free pool amino acid from the cell which were accompanied with the cell death. On the basis of these results, physiological changes occuring in the yeast cell are discussed.
