Sterol carrier protein 2 and fatty acid-binding protein. Separate and distinct physiological functions.
Sterol carrier protein 2 (SCP-2) participates in the microsomal conversion of lanosterol to cholesterol, in the conversion of cholesterol to cholesterol ester, and in intracellular cholesterol transfers. The stoichiometry of binding between cholesterol and SCP-2 is 1:1. However, reports have appeared attributing sterol carrier protein activity to a protein preparation identical to hepatic fatty acid-binding protein (FABP). Therefore, the present investigation was conducted to compare homogeneous preparations of FABP and SCP-2 with respect to their capacities to participate as carrier proteins in reactions involving sterols or fatty acids. The results show that SCP-2 and FABP have separate and distinct physiological functions, with SCP-2 participating in reactions involving sterols and FABP participating in reactions involving fatty acid binding and/or transport. Furthermore, there is no overlap in substrate specificities, i.e. FABP does not possess sterol carrier protein activity and SCP-2 does not specifically bind or transport fatty acid. As long as only small quantities of organic solvent (1.6 volume %) were used for substrate addition, the sterol delta 7-reductase liver microsomal assay for SCP-2 correlated well with the physiologically relevant assays employed in the reconstituted adrenal system. The sterol carrier protein activity previously attributed to rat hepatic FABP is explained by the presence of significant quantities of propylene glycol (15 volume %) or Tween 80 in the assay procedure.
D000311:Adrenal Glands / Q000378:metabolism; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D002352:Carrier Proteins / Q000502:physiology*; D002784:Cholesterol / Q000378:metabolism; D002788:Cholesterol Esters / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D019301:Oleic Acid; D009829:Oleic Acids / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism; D044925:Oxidoreductases Acting on CH-CH Group Donors; D010940:Plant Proteins; D011284:Pregnenolone / Q000096:biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains
D000596:Amino Acids; D001095:Arachidonic Acids; D002352:Carrier Proteins; D002788:Cholesterol Esters; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D009829:Oleic Acids; D010940:Plant Proteins; C033144:lathosterol delta-5-dehydrogenase; C072087:sterol carrier proteins; D016718:Arachidonic Acid; D019301:Oleic Acid; D011284:Pregnenolone; D002784:Cholesterol; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors