[Relationship between aeration and sterol distribution in yeasts]

The content of sterols in yeast organisms changes noticeably depending on the cultivation conditions. This content sharply decreases when the cells are transferred from aerobic to anaerobic conditions. The proportion between various sterol fractions also changes. The content of bound sterols under aerobic conditions reaches 85-90% of the total sterol content; that of free sterols is only 10-15%. Under anaerobic conditions, the quantity of bond sterols decreases to 70-75% while that of free sterols increases respectively to 25-30%. The fraction of free sterols increases whereas that of bound sterols decreases under aerobic conditions if oleic acid is added to the cultural broth. The content of all of the sterol fractions increases if oleic acid is added under anaerobic conditions. The same correlation is found when ergosterol is added to the medium under anaerobic conditions. Only the total sterol content and the content of sterol esters increase, rather than the content of free sterols, when cholesterol is added to the medium under anaerobic conditions.