CHARACTERIZATION OF THE DIACYLGLYCEROL ACYLTRANSFERASE ACTIVITY IN THE MEMBRANE-FRACTION FROM A FUNGUS

In an attempt to clarify the mechanism of lipid accumulation in Mortierella ramanniana var. angulispora, diacylglycerol acyltransferase (DGAT) in the membrane fraction from this fungus was characterized. The enzyme had an optimum pH of 7.0-7.5, and enzyme activity was blocked by SH-reagents. Metal ions were not essential for maintaining DGAT activity. n-OCtyl-beta-D-glucoside, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate and Tween 80 were found to preserve activity, while Triton X-100 and sucrose monolaurate inhibited it. As the inhibition of DGAT activity by Triton X-100 was overcome by the addition of diacylglycerol (DG), the dependency of DGAT activity on exogenous DG was determined in the presence of 0.1% Triton X-100. DGAT activity in the membrane fraction was traced in fungi cultured for different time periods or in media at different carbon to nitrogen (C/N) ratios. Although the increase in total lipid content with culture time was accompanied by an increase in DGAT activity, total lipid changes related to changes in C/N ratio did not correlate with DGAT activity. Factors other than DGAT activity in the membrane fraction would appear to be involved in the regulation of total lipid content in this fungus.