Chylomicron-lipid-splitting activity in homogenates of rabbit polymorphonuclear leukocytes

¹ Department of Medicine, New York University School of Medicine, New York City

Evidence for hydrolysis of chylomicron-triglyceride was sought in homogenates of polymorphonuclear leukocytes obtained from rabbit peritoneal exudates. Such activity was found using chylomicra from human thoracic duct lymph. Release of fatty acid was greatest at pH 4.8 and a triglyceride concentration of 5 mm. Most of the activity was found associated with particulate fractions of the homogenate. Almost 50% of the total activity occurred in association with the granules (lysosomes) of the leukocytes. Repeated freezing and thawing of whole homogenate or its particulate fractions resulted in an increase in activity of approximately 50%. The activity was inhibited by phosphate and NaF but not by protamine or iodoacetate. It is concluded that homogenates of leukocytes contain an acid glycerolester hydrolase, which splits triglycerides of naturally occurring lipoproteins. The intracellular distribution of the activity suggests that it is at least in part lysosomal in origin.

Key Words: hydrolysis of chylomicron lipid • lipid metabolism by leukocytes • triglycerides • acid lipase activity • lysosomes

Submitted on March 8, 1965