Purification and properties of sterol carrier protein2.

The present article describes the purification and properties of sterol carrier proteinz (SCPz), which has been purified to apparent homogeneity from rat liver 303,000 X g soluble supernatant ( s 3 0 3 ) .SCPZ activates the microsomal conversion of 4,4-dimethyl-A8-cholestenol to CZ, sterol and the microsomal conversion of 7dehydrocholesterol to cholesterol.The purification factors achieved during SCPZ purification were essentially the same (1400-to 1500-fold) for both substrates.In contrast to SCPl, SCPZ did not activate the microsomal conversion of squalene to lanosterol.Evidence for the homogeneity of the purified SCPz includes the following: (i) a single band in basic, acidic, and sodium dodecyl sulfate polyacrylamide gel electrophoresis, (ii) a single band in analytical isoelectric focusing, and (iii) exact correspondence between SCPz activity and stained protein absorbance in polyacrylamide gel electrophoresis.SCPz is a basic protein (PI E 8.6) with a molecular weight of 13,500, as measured by sodium dodecyl sulfate polyacrylamide gel electrophoresis.The most abundant amino acid is lysine (14.0 mole 8).In addition, SCP2 has no arginine or tyrosine.