Isolation of a phospholipase-A2-like protein from human fetal intestine. Lysis of erythroid cells from bovine liver by this protein and porcine phospholipase A2

Abstract

Extracts of human fetal intestine contain factors that can stimulate or inhibit thymidine incorporation into fetal bovine erythroid cells. An inhibitory factor was purified to homogeneity by gel-permeation and reversed-phase high performance liquid chromatography. The inhibitory action was due to cell lysis. The first 25 amino acids of the N-terminal segment were identical to the human lung and pancreatic phospholipase A2. The isolated protein released arachidonic acid from 2-arachidonyl phosphatidylcholine. Porcine phospholipase A2 had the same effects as the intestinal protein, including its tissue-specific lysis of fetal bovine liver erythroid cells. No decrease of thymidine incorporation was seen in fetal bovine intestinal cells, 3T3 cells, or K562 cells incubated with the porcine enzyme. No release of hemoglobin or cell lysis was observed with human erythrocytes or fetal bovine erythrocytes. Porcine and bee phospholipases, which have low sequence homology, are nearly equipotent in inhibiting thymidine incorporation, whereas melittin and β-bungarotoxin were less active than the pancreatic enzyme. These results support the tissue-specific effects observed with other phospholipases A2. The high sensitivity of liver erythroid cells towards some phospholipases A2 suggest that these enzymes may be involved in the elimination of hepatic erythroid cells at the end of gestation.Key words: erythropoiesis, tissue remodeling, fetal liver, extracellular phospholipase A2, erythroblast maturation.