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The effect of sterol carrier protein-2 (SCP-2) on dolichol biosynthesis by rat liver microsomes was investigated. cis-Prenyltransferase activity was stimulated 7-fold in the presence of 5 micrograms of purified SCP-2/mg of microsomal protein, which was similar to the increase obtained by adding detergent. The polyisoprenoid pattern obtained in the presence of SCP-2 was the same as that present in rat liver, in contrast to the pattern appearing upon incubation of microsomes with detergent, which gave shorter polyisoprenoids. Like SCP-2, the cytosolic fraction from rat liver also stimulated cis-prenyltransferase. Incubation with cytosol pretreated with anti-SCP-2 showed no stimulatory effect and led to the accumulation of shorter polyisoprenoids. SCP-2 had no appreciable effect on polyprenol alpha-saturase, dolichol kinase, dolichyl phosphate phosphatase, or acyl-CoA:dolichol acyltransferase. The results demonstrate that SCP-2 greatly stimulates and may regulate the condensation reactions mediated by cis-prenyltransferase in the process of dolichol biosynthesis and permits polymerization of the polyisoprenoid to its natural chain length.

The content of dolichol and dolichyl phosphate in various human organs was analysed using autopsy samples. The reliability of these measurements was demonstrated by comparison with values for fresh biopsy material. Dolichol was present in all tissues investigated and the content was highest in the adrenal gland, pancreas, pituitary gland, testis and thyroid gland, ranging between 1.5 and 7.1 mg/g tissue. Dolichyl-P was detected in the various organs in highly variable amounts, ranging between 1 and 9% of the total dolichol content. While the main pattern of isoprene composition for dolichol and dolichyl-P was similar in individual organs, some variation was observed between tissues. Dolichol represents the largest lipid component in the pituitary gland, exceeding the total phospholipid content. The high concentrations of dolichol and dolichyl-P in human organs indicate that these lipids may play important roles in physiological and pathological cellular functions.

Fil:Behrens, N.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Parodi, A.J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.