The intracellular location of various enzymes involved in the metabolism of phospholipids of Candida albicans was studied. Among the biosynthetic enzymes, phosphatidylserine synthetase was found to be localized in the microsomes; choline kinase and ethanolamine kinase were cytosolic; acyltransferase was localized in the paniculate fraction and glycerol kinase and phosphatidic acid phosphatase were distributed in both the microsomal and cytosolic fractions. Phospholipase A and phospholipase C were abundant in the microsomes and phospholipase C was also detected in the cytosol. Lysophospholipase and glycerophosphocholine diesterase were distributed mainly in the mitochondria. Lipase activity was also detected in this fungus. Based on the enzymes detected in this study we have postulated pathways of phospholipid metabolism in C. albicans.Phospholipids are vital structural and functional entities of biomembranes [6] and their metabolism is related to the formation and functions of membrane components [ 1 ]. Biosynthesis of phospholipids occurs mainly via the Kennedy and CDP-diacylglycerol pathways, in addition to alternate routes such as base exchange, methylation, acylation and deacylation reactions. Phospholipid degradation takes place by three main pathways. The first includes phospholipase A, lysophospholipase and glycerophosphocholine diesterase, the second involves phospholipase C, and the third involves phospholipase D and results in the formation of phosphatidic acid. Phosphatidic acid is used either to synthesize triglycerides, or is degraded by lipase for conversion to glycerol-3-phosphate by glycerol kinase. The presence of these pathways has been established in mammalian systems, and to some extent in fungi [8,12,23], but in Candida albicans the information is restricted to extracellular phospholipases [4,19]. This communication describes the identification and subcellular distribution of enzymes of phospholipid metabolism in C. albicans. METHODS ChemicalsRadiolabelled (3H)-glycerol (sp. act. 2-50 mCi mmol-1), (3H)-ethanolamine (sp. act.

Lipids constituted around 5% of the dry weight in Candida albicans 3153, while sterols and phospholipids accounted for 1.2% and 1.1% respectively. Phospholipids were mainly localized in the microsomal fraction; p hosp ha tid y lserine (PS) , p hos p hatid y lcholine ( P o , p hos p hatid y le t hanolamine (PE) and p hosp hatidy linositol (PI) were the major phospholipids. Incorporation studies with [ 14C]acetate and [32P]orthophosphoric acid demonstrated that PS was synthesized at the highest rate followed by PC, PE and PI. There was little difference in either the content or the rate of biosynthesis of PC, PE and PI. Incorporation of labelled serine, ethanolamine and choline revealed serine to be a precursor for PC, PE and PS, ethanolamine for PC and PE, and choline for PC biosynthesis only.

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