CHARACTERIZATION OF CELLULAR AND ELEVATED SERUM PHOSPHOLIPASE-A2 ACTIVITIES WITH A COMPARISON OF 2 METHODS

The phospholipase A assay of Hoffmann et al based on the enzymatic pho tometric determination of the fatty acids liberated from soy-bean phos pholipids was compared with the fluorometric assay of Thuren et al. wh ere a synthetic pyrene-labelled substrate is used. Sera from patients with suspected pancreatitis or sepsis were studied. High values compar ed well while the Hoffmann method was not sensitive enough to detect s lightly elevated values in sera from patients with suspected pancreati tis. The phospholipase A2 activities from enzymes purified from human duodenal juice, human sera from patients with sepsis and rat liver mit ochondria were characterized in regard to activity towards several syn thetic pyrene-labelled substrates, activation by Ca2+ and inhibition b y Sr2+ and Mg2+. The enzyme from serum was distinctly different from b oth the pancreatic secretory and the mitochondrial ones, both in its s ubstrate specificity pattern and in being most strongly inhibited by M g2+.