Properties of an acid cholesteryl ester hydrolase inhibitor from rat serum.
The inhibitory effect of a protein isolated from rat serum on lysosomal acid cholesteryl ester hydrolase (acid CEH; EC.3.1.1.13) activity was studied. An inhibitor was purified from rat serum following ultracentrifugation and heat treatment using column chromatography on Sephacryl S-200 and ultrafiltration. The purified inhibitor appeared as a single protein band in sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The molecular weight of the inhibitor was 28,000 Daltons as judged by gel filtration on Sephacryl S-200 and SDS-polyacrylamide gel electrophoresis. The purified inhibitor was shown to be apolipoprotein A-I (apo A-I), the major apolipoprotein of high-density lipoprotein (HDL), using immunoprecipitation with rat anti-apo A-I immunoglobulin (Ig)G. Inhibition of acid CEH activity by apo A-I was dependent on the concentration of apo A-I. The values of Vmax obtained were similar with or without apo A-I. Apo A-I of various other mammalian species, including human, bovine and rabbit, also inhibited acid CEH activity. Other apolipoproteins, such as apo A-II and apo B, also showed inhibiting activity. On the other hand, apo A-I had no effect on the activity of other enzymes found in lysosomes, such as cathepsin D, beta-glucuronidase and acid phosphatase. The results suggest that apolipoproteins may play a role in the regulation of hydrolysis of cholesteryl esters in lipoproteins, that have been transferred to the liver, and that the inhibition of acid CEH activity by apo A-I may be a characteristic of the lipid-binding protein or be due to changes of the lipid/water interface.
Tanaka
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M
Showa College of Pharmaceutical Sciences, Tokyo, Japan.
Iio
T
T
Tabata
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T
D000818:Animals; D016632:Apolipoprotein A-I; D001054:Apolipoproteins A / Q000097:blood*; D002850:Chromatography, Gel; D006868:Hydrolysis; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D002787:Sterol Esterase / Q000037:antagonists & inhibitors* / Q000378:metabolism
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D002787:Sterol Esterase