Abstract
A Ca 2+-dependent lysophospholipase D activity in microsomal preparations from the rabbit kidney medulla hydrolyzes the choline moiety from 1- O-[9,10- 3 H]hexadecyl-2-lyso- sn-glycero-3-phosphocholine (lyso-PAF) to form 1-O-[9,10-[ 3H] hexadecyl-2- lyso-sn- glycero-3-P ; the latter is subsequently dephosphorylated by a phosphohydrolase to 1- O-[9,10- 3 H]hexadecyl- sn-glycerol. Sodium vanadate, which is known to inhibit phosphohydrolases, reduces the proportion of hexadecylglycerol and increases the formation of hexadecyllysoglycerophosphate. Essentially no hydrolysis occurs when the sn-2 position of the hexadecyllysoGPC substrate contains an acyl moiety. The lysophospholipase D in rabbit kidney is of microsomal origin and has a broad pH optimum between 8.0 and 8.8, with the activity decreasing sharply from pH 7.6 to 7.2. Wykle et al. (Biochim. Biophys. Acta 619 (1980) 58–67) have previously demonstrated the existence of a microsomal lysophospholipase D (specific for ether lipid substrates) in rat tissues that requires Mg 2+ and exhibits a pH optimum of 7.2; high activities of the Mg 2+-dependent lysophospholipase D were found in liver and brain, but not in kidney. In contrast to the Mg 2+-dependent lysophospholipase D in rat tissues, the renal enzyme from rabbits requires Ca 2+ (5 mM), whereas Mg 2+ (5 mM) exhibits little stimulatory action. Under optimal assay conditions (0.1 M Tris-HCl (pH 8.4)/5 mM CaCl 2), lysophospholipase D in the rabbit kidney medulla has an activity of 2.7 nmol/min per mg protein compared to 0.9 nmol/min per mg protein for the lysophospholipase D in the rat kidney medulla (0.1 M Tris-HCl (pH 7.2)/5 mM MgCl 2). The Ca 2+-dependent lysophospholipase D is highest in the liver and kidney medulla from rabbits, but is very low in rat tissues; similar activities were found in male and female rabbits. Our data indicate that the divalent metal ion requirements for expression of maximum lysophospholipase D activities can differ markedly among animal species and also suggest the microsomal Ca 2+-dependent lysophospholipase D is an important catabolic route for lyso-PAF metabolism in rabbit renomedullary tissue.
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Schedule a callMore From: Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism
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