AN ANIMAL-CELL MUTANT WITH A DEFICIENCY IN ACYL ALKYL-DIHYDROXYACETONE-PHOSPHATE REDUCTASE-ACTIVITY - EFFECTS ON THE BIOSYNTHESIS OF ETHER-LINKED AND DIACYL GLYCEROLIPIDS/

In the accompanying paper (James, P. F., and Zoeller, R. A. (1997) J. Biol. Chem. 272, 23532-23539), we reported the isolation of st series of mutants from the fibroblast-like cell line, CHO-K1, that are defici ent in the incorporation of the long chain fatty alcohol, hexadecanol, into complex lipids, All but one of these mutants, FAA.K1B, were defi cient; in long-chain-fatty alcohol oxidase (FAO) activity. We have fur ther characterized this FAO(+) isolate. FAA.K1B cells displayed a 40% decrease in [9,10-H-3]hexadecanol uptake when compared with the parent strain, Although incorporation of hexadacanol into the phospholipid f raction was decreased by 52%, She cells accumulated label in alkylglyc erol (20-fold over wild type), The increase in 1-alkylglycerol labelin g corresponded to a 4-fold increase in alkylglycerol mass. Short term labeling with P-32(i) showed a 45-50% decrease in overall phospholipid biosynthesis in FAA.K1B, Both diacyl- and ether-linked species were a ffected, suggesting a general defect in phospholipid biosynthesis. Mut ant cells were able to partially compensate for the decreased. biosynt hesis by decreasing tile turnover of the phospholipid pools, The prima ry lesion in FAA.K1B was identified as a 95% reduction in acyl/alkyl-d ihydroxyacetone-phosphate reductase activity, Whole cell homogenates f rom FAA.K1B were unable to reduce either acyl-dihydroxyacetone phospha te (DHAP) or alkyl-DHAP, supporting the notion that the reduction of t hese two compounds is catalyzed by a single enzyme, These data suggest that the biosynthesis of diacyl phospholipids, in Chinese hamster ova ry cells, begins with the acylation of dihydroxyacetone phosphate as w ell as glycero-3-phosphate and that the ''DHAP pathway'' contributes s ignificantly to diacyl glycerolipid biosynthesis, Also, the severe red uction in acyl/alkyl-DHAP reductase activity in FAA.K1B resulted in on ly a moderate decrease in ether lipid biosynthesis, These latter data together with the observed increase in alkylglycerol levels support th e existence of a shunt pathway that is able to partially bypass the en zymatic lesion.