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Abstract
The positional specificity of the phospholipase A in human gallbladder epithelium was studied by using biosynthetically radiolabeled diacylphosphoglycerides as substrates. Diacylphosphoglyceride in 14C-palmitic acid-labeled, autoclaved E. coli was hydrolyzed under the formation of monoacylphosphoglyceride and fatty acid that were both radiolabeled. In contras:, diacylphosphoglyceride in 14C-oleate-labeled bacteria was hydrolyzed so as to give radiolabel in the fatty acid only. Since 14C-palmitate occupies predominantly the 1-acyl position and 14C oleate the 2-acyl position of the major E. coli diacylphosphoglycerides, these findings suggest that: 1) the phospholipase attacks the 2-position of diacylphosphoglycerides, and 2) a complete deacylation of diacylphosphoglycerides in the gallbladder wall is brought about by the combined action of phospholipase A2 and a lysophospholipase, the latter being able to hydrolyze the 1-acyl-lysophosphoglyceride. It appears, therefore, that the biochemical prerequisites for a local formation and degradation of lysolecithin in the gallbladder itself are met by the positional specificity of the enzymes present. This finding further substantiates the hypothesis that lysolecithin is an adjustable mediator of aseptic cholecystitis.