Topography of rat hepatic microsomal enzymatic components of the fatty acid chain elongation system.
The orientation of the condensing enzyme, the beta-hydroxyacyl-CoA dehydrase, and the trans-2-enoyl CoA reductase within the rat liver microsomal membrane was investigated by the use of impermeant inhibitors of enzyme activity: trypsin, chymotrypsin, subtilisin, mercury-dextran, and anti-beta-hydroxyacyl-CoA dehydrase IgG. The activity of the condensing enzyme was inhibited more than 70% by various proteases and was completely inhibited by 80 microM mercury-dextran. Similar results were obtained for the trans-2-enoyl-CoA reductase activity. On the other hand, in the absence of detergent, proteases inhibited beta-hydroxyacyl-CoA dehydrase activity by 25-40%, while in the presence of detergent the inhibition increased to 65-90%. Furthermore, anti-beta-hydroxyacyl-CoA dehydrase IgG, which in the absence of detergent produced no inhibition, in the presence of detergent inhibited beta-hydroxyacyl-CoA dehydrase activity by more than 80%; under identical conditions, preimmune IgG caused a 13% inhibition. Microsomes used throughout this study displayed greater than 90% latency with respect to mannose-6-phosphatase activity, indicating that the microsomes were intact. Latency was not affected by the proteases, by mercury-dextran, or by the presence of the enzyme assay components. These results suggest that both the condensing enzyme and the reductase are present on the cytoplasmic surface of the membrane, whereas the beta-hydroxyacyl-CoA dehydrase is embedded in the microsomal membrane.
Osei
P
P
Department of Pharmacology, University of Connecticut Health Center, Farmington 06032.
Suneja
S K
SK
Laguna
J C
JC
Nagi
M N
MN
Cook
L
L
Prasad
M R
MR
Cinti
D L
DL
D044944:Acyl-CoA Dehydrogenases; D000818:Animals; D002451:Cell Compartmentation; D004746:Enoyl-CoA Hydratase / Q000378:metabolism; D044943:Fatty Acid Desaturases / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism*; D007158:Immunologic Techniques; D008862:Microsomes, Liver / Q000201:enzymology* / Q000648:ultrastructure; D010447:Peptide Hydrolases / Q000494:pharmacology; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D051381:Rats; D013439:Sulfhydryl Reagents / Q000494:pharmacology
D005227:Fatty Acids; D013439:Sulfhydryl Reagents; D044943:Fatty Acid Desaturases; D044944:Acyl-CoA Dehydrogenases; C100154:acyl-CoA dehydrogenase (NADP+); C023553:mannose-6-phosphatase; D010744:Phosphoric Monoester Hydrolases; D010447:Peptide Hydrolases; D004746:Enoyl-CoA Hydratase