Human milk lipases. I. Serum-stimulated lipase.

Lipase activity has previously been demonstrated in human milk. This study shows that there are two separate triglyceride lipases in human milk. One is mainly in the skim milk and is stimulated by bile salts; the other is mainly in the cream and is inhibited by bile salts but stimulated by serum. The serum-stimulated lipase was purified by affinity chromatography on heparin-substituted Sepharose 4B. This gave a 9500-fold purification over whole milk. Although polyacrylamide gel electrophoresis showed that the enzyme was not purified to homogeneity, it had the highest specific activity so far reported for a human serum-stimulated lipase. The purified enzyme was free from bile salt-stimulated lipase activity and had the characteristics of other serum-stimulated or so-called lipoprotein lipases. Thus, it was almost completely inhibited by 1 M NaCl. The purified enzyme was active against tributyrylglycerol also in the absence of exogenous serum factors.