Sterol carrier protein adrenal

Fig. 2. General scheme for transduction of ACTH signal from plasma membrane to mitochondria in the adrenal cortex. CHX, cycloheximide TG. triglyceride CE, cholesterol ester Lts, leukotrienes PGs, prostaglandins SCP2, sterol carrier protein PE, PC, PI, phosphatidyl ethanolamine, choline and inositol (from Ref. 25, with permission).

Since FABP is not capable of releasing cholesterol from adrenal lipid droplets or stimulating the utilization of endogenous mitochondrial cholesterol for pregnenolone production (see above), it is clear that FABP is not involved as a sterol carrier protein in a physiological sense [50]. Consistent with this finding is the observation of Mishkin et al. [52] that FABP does not bind sterol. It is also clear that the... 

Fig. 8 is a schematic diagram of a cell which shows the known sites in which sterol carrier proteins are involved in cholesterol biosynthesis, utilization and intracellular transfer. SCP, participates in the conversion of squalene to lanosterol and SCP2 participates in the conversion of lanosterol to cholesterol, the conversion of cholesterol to cholesterol ester by ACAT, and probably also in the conversion of cholesterol to 7a-hydroxycholesterol. SCPj transfers cholesterol from cytoplasmic lipid inclusion droplets to mitochondria in the adrenal and SCPj also translocates cholesterol from the outer to the inner mitochondrial membrane. 

Many steps in sterol biosynthesis are stimulated by a sterol carrier protein. The identity of this protein is not known but its effect seems to be widespread. A rat liver carrier protein also affects adrenal and brain systems. Substitution by a carrier protein from Tetrahymena pyriformis gave partial stimulation with the rat liver preparation. The function of this molecule may be regulatory. At low levels of carrier protein, sterol biosynthesis is mainly via A -sterols, whereas at higher levels the 24,25-dihydro-derivatives are preferred. Apo-lipoprotein II (and to a lesser extent I) produce a similar effect. ... 

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