BIOSYNTHETIC MECHANISM OF SN-2,3-DI-O-PHYTANYLGLYCEROL, CORE MEMBRANE LIPID OF THE ARCHAEBACTERIUM HALOBACTERIUM-HALOBIUM

The biosynthetic mechanism of the membrane core lipid of the archaebacterium Halobacterium halobium was studied by feeding 18O-labeled glycerol, chirally deuterated glycerol, and deuterated glucose to the culture, and subsequent 13C, 1H, and 2H NMR analyses of the isotopically enriched 2,3-di-Ophytanylglycerol. A 18O-chase experiment showed that the oxygen atom of sn-C-3 of glycerol is retained ultimately in xn-2,3-di-Ophytanylglycerol, thereby suggesting its nucleophilic nature in the ether-forming reaction. Efficient and stereospecific incorporation of the C-6 of glucose and sn-C-3 of glycerol into the sn-C-lposition of the lipid strongly implied that (1) the Entner-Doudoroff pathway operates in H. halobium and (2) stereochemical inversion apparently takes place at the C-2 position of glycerol to form 2,3-di-O-alkylated lipids. Chase studies of the C-2 hydrogen further suggested an oxidation and a reduction processes are responsible for the inversion of configuration at C-2 of the glycerol moiety. A stepwise alkylation mechanism is postulated. © 1990, American Chemical Society. All rights reserved.