INFLUENCE OF BIOTIN ON THE LIPID-COMPOSITION OF PLASMA-MEMBRANES FROM HYPOMYCES-CHLORINUS

Subfractions of microsomal membranes from the biotin heteroauxotroph Hypomyces chlorinus Tul., cultured in media containing optimal or suboptimal levels of the vitamin, were isolated using a two-phase polymer system and characterized as plasma membrane-enriched on the basis of absence of Zn2+-induced aggregation, enrichment of appropriate enzyme markers, and phosphotungstic acid - chromic acid staining. The protein/lipid ratio of membranes from the biotin-sufficient and -deficient cultures was 2; the phospholipid content was 126 and 181 μg/mg protein; and the sterol/phospholipid molar ratios were 0.38 and 0.16, respectively, with ergosterol as the predominant sterol. The lipids were qualitatively similar in the plasma membrane fractions from the two treatments. Ergosterol content of the membrane fractions from mycelium cultured in low biotin medium was 40-100% less than that from the corresponding biotin-sufficient cultures. A nonphosphorus glycolipid was the predominant lipid of the plasma membranes from both treatments.