Characterization of cellular and elevated serum phospholipase A2 activities with a comparison of two methods

The phospholipase A assay of Hoffmann et al based on the enzymatic photometric determination of the fatty acids liberated from soy-bean phospholipids was compared with the fluorometric assay of Thurén et al. where a synthetic pyrene-labelled substrate is used. Sera from patients with suspected pancreatitis or sepsis were studied. High values compared well while the Hoffmann method was not sensitive enough to detect slightly elevated values in sera from patients with suspected pancreatitis. The phospholipase A2 activities from enzymes purified from human duodenal juice, human sera from patients with sepsis and rat liver mitochondria were characterized in regard to activity towards several synthetic pyrene-labelled substrates, activation by Ca2+ and inhibition by Sr2+ and Mg2+. The enzyme from serum was distinctly different from both the pancreatic secretory and the mitochondrial ones, both in its substrate specificity pattern and in being most strongly inhibited by Mg2+.