Add time:08/20/2019         Source:sciencedirect.com

1.1. The characteristics of acid lipase with 4-METHYLUMBELLIFERYL OLEATE (cas 18323-58-5) as substrate and acid cholesteryl esterase with cholesteryl [1-14C]oleate as substrate were investigated in homogenates of human leucocytes, fibroblasts and liver. The substrates were encapsulated in egg yolk lecithin vesicles and assays were developed which were linear with amount of protein and with time.2.2. With 4-methylumbelliferyl oleate as substrate, a pH optimum of 4.0 was found in all preparations. Half-maximal activity was obtained in leucocytes at 7 μM, fibroblasts at 4 μM and liver at 14 μM. Similar inhibition of the enzyme from the three sources was observed with various inhibitory compounds. It is concluded that the hydrolysis of 4-methylumbelliferyl oleate is catalyzed by one enzyme common to the three cell types.3.3. With cholesteryl [1-14C]oleate as substrate, the pH optima for leucocytes, fibroblasts and liver were 4.5 4.0 and 3.5, respectively. Furthermore, the concentration necessary for half-maximal activity for leucocytes, fibroblasts and liver was 23, 25 and 20 μM, respectively. The inhibition percentages with the different substances were different for the three cell types. It is suggested that these differences between the three cell types might be due to the different environments of the enzyme.4.4. Comparing the results of the hydrolysis of 4-methylumbelliferyl oleate with those of the hydrolysis of cholesteryl [1-14C]oleate, we concluded that two different proteins (or one protein which possesses two distinct catalytic sites for both substrates) are involved.

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