Although a wealth of cultural and biochemical data has been published on sterol synthesis in whole and fractionated cellular systems, little information is available on the physiological function of sterols in fungi. That these compounds are of great metabolic importance is demonstrated by the universality of their distribution and synthesis. It is reasonable to theorize that sterols must play a vital role in cell metabolism otherwise non-sterol producing strains would have had a selective advantage in nature. Such would be the case because of the great demands sterol synthesis places for energy and carbon intermediates.
Previous studies (Starr and Parks, '62a,b) provided information pertaining to the effects of varying cultural conditions on the synthesis and final yield of sterols in yeast. In the accumulation of those data a relationship between respiratory activity and sterol synthesis was noted. It seemed propitious, therefore, to design additional experiments to ascertain any relationship between respiratory deficient forms, their induction, and the capacity of the organism for sterol formation. The results of these experiments are the subject of this paper. In addition, a theory is presented on the roIe of ergosterol in maintaining respiratory competency.