CHARACTERIZATION OF THE DIACYLGLYCEROL ACYLTRANSFERASE ACTIVITY IN THE LIPID BODY FRACTION FROM AN OLEAGINOUS FUNGUS

Diacylglycerol acyltransferase (DGAT) was examined as a key enzyme for triacylglycerol (TG) accumulation of an oleaginous fungus, Mortierell a ramanniana var, angulispora, Subcellular fractionation of the fungus showed that DGAT activity was highest in the lipid body fraction, whi ch occupied 77% of the recovered DGAT activity, DGAT activity in the l ipid body fraction was much higher than that in the membrane fraction in terms of both total activity and specific activity. Similar results were obtained with another homogenization method. After repeated wash ing of the lipid body fraction, DGAT activity in the lipid body fracti on was still larger than those in other fractions. The lipid body frac tion contained larger amounts of lipids, especially TG and diacylglyce rol. Moreover, the lipid body fraction had a specific set of polypepti des at 24, 29, and 59 kDa. These analyses of lipid and polypeptide com position suggested that the lipid body fraction represented a specific intracellular structure, presumably the lipid body. DGAT activity in the lipid body fraction had a similar characteristics to that in the m embrane fraction, although some differences in sensitivity to SH-reage nts were observed. Increase in DGAT activity in the lipid body fractio n was observed when lipids were accumulated in the fungus. On the othe r hand, DGAT activity in the lipid body fraction decreased when lipids were accumulated with an increase in carbon to nitrogen ratio in medi a.