1-O-alkyl-2-acetyl-sn-glycero-3-phosphate : phosphohydrolase activity in Tetrahymena pyriformis

Within the frame of the de novo formation of Platelet-Activating Factor in Tetrahymena, the occurrence as well as the properties of a lipid phosphate phosphohydrolase activity catalyzing the dephosphorylation of 1-O-alkyl-2-a cetyl-sn-glycero-3-phosphate was investigated. The activity was distributed in all the membrane fractions of the cell and in the cytosol. It showed pr eference for acyl-acetyl-sn-glycero-phosphate as well, and at a much lower level, for dipalmitoyl-glycero-phosphate. Mg2+ and Ca2+ caused a dose-depen dent inhibition, while F-, EDTA and EGTA had no effect. The enzymic activit y was linear for at least up to 60 min incubation time and up to 150 mu g p rotein. Microsomal activity exhibited two optimal pH areas, around 7.0 and 9.0, while mitochondrial activity showed one peak, at pH 7.0. Acyl-GP, acyl -acetyl-GP and alkyl-GP could replace alkyl-acetyl-GP in significant rates, while dipalmitoyl-GP, beta-GP, fructose-6-GP, p-nitrophenylphosphate, crea tine phosphate or ATP had no effect. Side phospholipose A(2) and C activiti es were also detected. Taking into account the presence of PAF and alkylace tylglycerol in the protozoan as well as the presence of a dithiothreitol- i nsensitive CDP-choline:cholinephosphotransferase activity that converts alk ylacetylglycerol to PAF, we suggest that the present phosphohdrolase activi ty may be involved in the de novo production of PAF within Tetrahymena.