Acid cholesterol ester and glycerol ester hydrolase activities. Evidence for the individuality of these enzymes in human mononuclear leucocytes.

ABSTRACT

Hydrolysis of cholesterol oleate and glycerol trioleate was measured in homogenates of human leucocytes at optimum pH of 4.0 and 5.25, respectively. Both enzyme activities appeared to reside in the 15,000 x g, 20-min fraction of mononuclear leucocytes. Solubilization of cholesterol ester hydrolase activity was strongly dependent on the detergent to protein ratio, showing optimal solubilization at weight ratios of 1.0 in cell homogenates and of 3.0 in the 15,000 x g, 20-min fraction, whereas solubilization of glycerol ester hydrolase was independent to protein ratio over the tested range of 0.3 to 5.8. Using a sequential solubilization procedure, about 60% of the granule proteins as well as 88% of glycerol ester hydrolase activity were solubilized at a detergent to protein ratio of 0.3, whereas cholesterol ester hydrolase activity was solubilized from the remaining membranes at a ratio of about 3.0. Thus, the acid glycerol ester hydrolase and acid cholesterol ester hydrolase were related to different proteins. Since solubilization of cholesterol ester hydrolase required drastic treatment, it is suggested that this enzyme is related to a protein within the lysosomal membrane.