et Biophysics Acta ELSEVIER Biochimica et Biopbysica Acta 1215(1994) 337-340 Possible role of cafcium in phospho~ipid synthesis of Mic~~s~~~urn gypseum Shailendra Giri, Nandini Mago, Anu Bindra, G.K. Khuller * zyxwvutsrqponmlkjihgfedcba Department of Biochemistry, Postgraduate Institute of Medical Education and Research, Chandigarh-160012, India Received24 February 1994; revised 4 July 1994 Abstract The effect of calcium on lipid synthesis in M icrosporum gy psew n was examined by growing these cells in calcium supplemented (1 mM to 10 mM) medium. Maximum incorporation of [14C]acetate into total lipids and phospholipids was observed in cells grown with 6 mM calcium. This was probably due to a 3-fold increase in total calcium levels as incorporation of label was inhibited in total lipids (33%) and phospholipids (20.5%) in calcium-grown cells which were preincubated with the calcium specific chelator ethylene glycoibis ( &aminoethyl ester) ~,~,~‘,~‘,-te~a~tate (EGTA). Increased incorporation of [14C]acetate into phospholipi~ was further supported by increase in the activity of key phosphoiipid biosynthetic enzymes (glycerolkinase and glycerol-3-phosphate acyltransferase) as well as the increase in phospholipid content in calcium-grown cells, which suggests a correlation between increased calcium levels and phospholipid biosynthesis in M. gypseum. Keywords: Calcium; Phospholipid;Lipid synthesis; (M. gypseum) 1. Int~u~on Calcium functions universally as an intracellular mes- senger and regulates many physiological processes. Many of these functions are accomplished through the interaction of calcium with intracellular-binding proteins or receptors, such as calmodulin, which activates various enzymes and other cellular processes [1,2]. Calcium also stimulates sev- eral enzymes like proteases, phospholipases, endonuclease(s) involved in the catabolism of macro- molecules for the maintenance of cell structure and func- tion [3]. The intracellular-free calcium concen~ation in resting cells is very low, which may arise from the extra- cellular medium, intracellular calcium stores (calcisomes) or a combination of both when the cells are activated [4]. Role of different second messengers, i.e., cyclic AMP and calmodulin in lipid metabolism has been investigated to a limited extent [5,6]. Recently, CAMP has been reported to influence lipid biosynthesis in mast cells 171, hamster fibroblasts [8] and fungi [6]. Although, the role of calcium in membrane fluidity is well established, its indirect role in phospholipid metabolism has recently been indicated in * Corresponding author. ~y&o~ucter~u~ s~e~~~ [9]. However, no info~ation is available with regard to the role of calcium on lipid metabolism in fungi, which are phylogenically close to eucaryotes. In this communication, we report for the first time the effect of supplemented calcium in the growth medium on the phospholipids of Microsporum gypseum, a human pathogenic fungi. 2. Materials and methods Radiolabelled [14C]acetate (spec. act. 60.3 m~i/mmol) was obtained from BARC, Bombay. ]3H]Glycerol (spec. act. 2.5 mCi/mmol) and [‘4C]glycero1-3-phosphate (spec. act. 170 mCi/mmol) were purchased from Amersham, UK. ATP, gly~rol-3-phosphate, acetyl-CoA and Dowex I-HCOO-x 8 (100-200 mesh) ion-exchange resin were obtained from Sigma, St. Louis, USA. The rest of the chemicals used were of analytical grade. 2.1. Growth of culture M. gypseum obtained from the Mycological Reference laboratory (School of Hygiene and Tropical Medicine, London) was grown in shake culture in Sabouraud’s broth US-27~/94/$07.~ 8 1994 Elsevier Science B.V. AR t-i&s reserved SSLX 0005-2760(94)00158-8