Phosphatidylmonoglucosyl diacylglycerol of Pseudomononas diminuta ATCC 11568. In vitro biosynthesis from phosphatidylglycerol and glucosyl diacylglycerol.

Phosphatidylmonoglucosyl diacylglycerol of Pseudomonas diminutu is biosynthesized from [14C]glycerolor 32Plabeled phosphatidylglycerol and [Wlglycerolor [‘4C]glucase-labeled 3-O-(ru-o-glucopyranosyl)-1,2-diacyl-sn-glycerol (glucosyl diacylglycerol) by a transphosphatidylation reaction. Diphosphatidylglycerol and kojibiosyl diacylglycerol which are substrates in a transphosphatidylation catalyzed by an enzyme from Streptococcus faecalis (faecium) do not function as substrates in the P. diminuta system even though they are structurally related to the natural substrates. CDP-dioleoylglycerol also is not a substrate. Glucosyl diacylglycerol from S. faecalis (fuecium) is about onefifth as active as a substrate as the glucosyl diacylglycerol from P. diminutu. The two glucosyl diacylglycerols differ only in their fatty acid composition. The rate of incorporation of either phosphatidylglycerol or glucosyl diacylglycerol into phosphatidylmonoglucosyl diacylglycerol is linear up to 30 min at both relatively low (36 and 41 PM) and high (116 and 120 PM) exogenous concentrations. Of the two substrates only glucosyl diacylglycerol could be administered in sufficient quantity to approach saturation of the transphosphatidylase. Optimal conditions for the reaction include a temperature of 25”, pH 7.6, and Triton X-100 concentration of 0.25% (4 mM). Triton X-100 at a concentration of 1 to 2% (16 to 32 mM) almost completely inhibits the biosynthetic reaction. A variety of characterization techniques and the stereochemistry of the substrates demonstrate that the structure of the in vitro synthesized phosphoglycolipid is 3-O-[6’(l”,2”-diacyl-3”-phosphoryl-sn-glycerol)-cu-o-glucopyranosyl]-1,2-diacyl-sn-glycerol.