Biosynthesis of 1-alkyl-sn-glycero-3-phosphate via adenosine triphosphate:1-alkyl-sn-glycerol phosphotransferase.

The pink portion of the rabbit harderian gland was found to be a rich source of ATP: I-alkyl-sn-glycerol phosphotransferase. The enzyme, associated with the microsomal fraction of the gland, exhibits a pH optimum of ‘7.1. ATP and Mg2f are absolute requirements for enzymatic activity; the apparent K,,, for Mg2+ATP is 1.6 mM. Manganese partially substituted for Mgz+, but the measured rate in the presence of Mn*f was only one-half of the rate determined in the presence of Mg2+. We identified the product of the reaction by chromatographic, chemical, and enzymatic techniques as I-alkyl-sn-glycero-3-phosphate. In incubations supplemented with coenzyme A, 1-alkyl-Z-acyl-sn-glycero-3phosphate was identified as the major product. High levels of monoacylglycerols, diacylglycerols, and their alkyl analogs did not inhibit phosphorylation of alkylglycerols. Attempts were made to show the phosphorylation of monoacylglycerols, but due to the high lipase activity in harderian gland microsomes, the results were inconclusive. The transfer of the terminal phosphate of ATP to position 3 of a I-alkyl-sn-glycerol was stereoselective; other isomeric alkylglycerols, as well as alkylethylene glycol and S-alkylglycerol were not phosphorylated by this system. These data demonstrate a way in which I-alkyl-sn-glycerols may enter the biosynthetic pathway that forms complex etherlinked glycerolipids.