Activation of detergent-solubilized diacylglycerol acyltransferase by anionic phospholipids.

Diacylglycerol acyltransferase (DGAT), which catalyzes the final step in triacylglycerol (TG) biosynthesis, is crucial for lipid accumulation and formation of lipid bodies in an oleaginous fungus, Mortierella ramanniana var. angulispora. Since solubilization of DGAT in the lipid body fraction from this fungus with 0.5% Triton X-100 gave very low recovery of the activity, some activation factors for solubilized DGAT activity were investigated. Addition of phospholipids, especially anionic phospholipids such as phosphatidic acid and phosphatidylserine, to the assay mixture greatly increased DGAT activity. The activation by these phospholipids was most prominent when 0.2% Triton X-100 was added to the assay mixture. The effect of phosphatidic acid was reproduced using DGAT fraction obtained by 0.5 M KCl elution on Mono S column chromatography. The results provide new insight on activation of DGAT during TG accumulation as well as optimal DGAT assay conditions for solubilized fractions.