Studies on the mode of action of sterol carrier protein in the dehydrogenation of 5-cholest-7-en-3 beta-ol.
Sterol carrier protein (SCP) (Ritter, M. C., and Dempsey, M.E. (1973) Proc. Natl. Acad. Sci. U.S.A. 70, 265-269) promotes the microsomal dehydrogenation of 5-cholest-7-en-3 beta-ol (lathosterol) to 7-dehydrocholesterol. This promotion occurs whether the substrate is exogenous or preincorporated into microsomes. Similarly, SCP promotes an intermembrane transfer of lathosterol from one microsomal population to another (Ishibashi, T., and Bloch, K. (1981) J. Biol. Chem. 256, 12962-12967). Here we present evidence for an SCP-mediated collisional interaction which results in the intermembrane transfer of sterol substrate and excludes a conventional substrate-carrier mechanism for SCP. Radioactive carboxymethyl SCP is shown to bind to microsomes and to anionic phospholipids but not to phosphatidylcholine. Treatment of microsomes with trypsin, but not with phospholipase A2, reduces SCP binding. Binding studies with small molecules substantiate the identity of SCP with Z-protein.
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002784:Cholesterol / Q000378:metabolism*; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005260:Female; D007536:Isomerism; D007700:Kinetics; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D010088:Oxidoreductases / Q000378:metabolism*; D044925:Oxidoreductases Acting on CH-CH Group Donors; D011485:Protein Binding; D051381:Rats; D013261:Sterols / Q000378:metabolism*; D014316:Tritium; D014357:Trypsin / Q000494:pharmacology
D002352:Carrier Proteins; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D013261:Sterols; C033144:lathosterol delta-5-dehydrogenase; D014316:Tritium; C001521:lathosterol; D002784:Cholesterol; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; D014357:Trypsin