PROPERTIES OF THE PHOSPHOLIPASE B FROM PENICILLIUM NOTATUM

Abstract

Phospholipase B from Penicillium notatum catalyzed rapid deacylation of purified egg lecithin, in the absence of any activators, when the substrate was ultrasonically dispersed. The rate of enzymic hydrolysis depended on the degree of dispersion of the substrate and also on its degree of unsaturation. Decrease in acyl ester groups was accompanied by release of water-soluble phosphate identified as glycerylphosphorylcholine; no lysolecithin was detected by thin-layer chromatography at any stage of the reaction. The optimum pH in acetate buffer was 4.0, and the apparent Kmwas 6.3 mM for the ultrasonically dispersed substrate. The enzyme attacked lysolecithin more rapidly than lecithin. Enzymic activity was not affected by iodoacetate, cyanide, or cystine, but was strongly inhibited by glutathione, cysteine, thioglycollate, ferrous and ferric ions, or by prolonged dialysis. Inhibition by glutathione was completely reversed by ferricyanide. These results suggest that the enzyme requires —S—S— linkages for activity.