Purification and characterization of SCP

SCPi participates in the enzymatic conversion of squalene to lanosterol by rat liver microsomes (cf. Chapter 1). It has been purified both in our laboratory [13] and by Ferguson and Bloch [14]. In Dr. Bloch s laboratory, the protein has been called supernatant protein factor or SPF [14-20]. It is a single polypeptide chain with a molecular weight of approximately 47000 dalton [14] (Table 1). The protein has an acidic p7. Recent evidence suggests that SCP] and SPF are one and the same protein [21]. 

By means of high resolution chromatographic techniques and mass spectrometry, it was shown that the major product (90%) formed when squalene was incubated with purified SCP, microsomes and cofactors (NADPH and FAD) was lanosterol [13]. While SCP] specifically activated the enzymatic conversion of squalene to lanosterol by liver microsomal membranes, it was not capable of activating reactions subsequent to the formation of lanosterol. Thus, the microsomal conversion of 

Characteristics of sterol carrier protein, (SCP,) and sterol carrier protein2 (SCP2) 

13500 -8.6 1. Lanosterol - cholesterol [21] 2. Reactions utilizing cholesterol as substrate [22,30,33] 3. Intracellular cholesterol transport [30,33] 

4-dimethyl-A -cholestenol to C27 sterols or of 7-dehydrocholesterol to cholesterol were not activated [13] nor the conversion of cholesterol to cholesterol ester [22], For SCPi to activate enzymatic reactions involving squalene and squalene-2,3-oxide, it was essential that microsomal membrane-bound enzymes be present. SCPi was catalytically inactive when it was incubated with squalene and cofactors in the absence of microsomes [13], 

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