The overall objective of this research grant is to study the participation of sterol carrier proteins in cholesterol biosynthesis, utilization and intracellular transfer. Specific aims related to the structure of sterol carrier proteins include the purification of sterol carrier protein2 (SCP2) from rat, pig and human tissues, the preparation on anti-SCP2 IgG, peptide mapping of SCP2, determination of the amino acid sequence of SCP2, and a detailed structural comparison of SCP2 to several other lipid transfer protein preparations. Specific aims related to the function of sterol carrier proteins include studies on the participation of SCP1 and SCP2 in cholesterol biosynthesis, the participation of SCP2 in intracellular cholesterol transport in rat liver, the participation of SCP(2) in the enzyme cholesterol 7Lambda-hydroxylase, the participation of SCP(2) in adrenal cholesterol transport and steroid hormone biosynthesis, functional comparisons of SCP(2) to various lipid transfer proteins, and regulatory interactions of cholesterol SCP(2) with the enzyme system which phosphorylates HMG-CoA reductase, the major rate limiting enzyme in cholesterol biosynthesis. A better understanding of the participation of sterol carrier proteins in cholesterol biosynthesis, utilization and intracellular transfer should lead to a better understanding of cholesterol metabolism in health and disease.