Participation of SCP2 in cholesterol biosynthesis

Sterol carrier protein 2 (SCP2) participates in the enzymatic conversion of lanosterol to cholesterol by rat liver microsomal enzymes. 

This is a complex enzymatic process which may involve as many as 20 steps [26] (Chapter 1). Available evidence, some of which is detailed below, is consistent with the conclusion that SCP2 acts as a carrier for all of the intermediates involved in this pathway between lanosterol and cholesterol. 

As determined by SDS-polyacrylamide gel electrophoresis, purified SCPj has a molecular weight of 13 500 (Table 1). 

A similar kinetic approach has been used to measure the specific activity of rat liver cytosol or of protein fractions obtained during the purification of SCP2 [21]. As with purified SCP2, the velocity of cholesterol formed is a hyperbolic function of the amount of cytosol protein present. As before, a straight line is obtained when the velocity of cholesterol formation is plotted as a function of cholesterol formed per mg of rat liver cytosol [21]. The purification factor for SCP2 can be calculated from X intercept for rat liver cytosol/2f intercept for purified SCP2. Using this approach [21], a purification factor of 1300-1400-fold was obtained. 

This mathematical procedure is, to the best of our knowledge, the first procedure to be described for the quantitative kinetic analysis of a carrier protein in an enzyme reaction [21]. 

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Participation of SCP2 in cholesterol biosynthesis (a) General remarks... 

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