Phenotypic differences in expression of cytochrome P-450g but not its mRNA in outbred male Sprague-Dawley rats.
Cytochrome P-450g was isolated from livers of adult male Sprague-Dawley (CD) rats. Antibody to P-450g cross-reacted with several proteins in Western blots of liver microsomes from male CD rats. An immunospecific antibody was prepared by adsorption over immunoaffinity columns of Sepharose-bound solubilized rat liver microsomes from female CD and male Fischer 344 rats containing little or no P-450g. The immunopurified antibody recognized a single protein on Western blots of liver microsomes from male CD rats with an electrophoretic mobility identical to that of P-450g. Using this antibody, P-450g was shown to be male specific in the CD rat and expressed at maturity. Adult male CD rats were shown to fall into two distinct populations, those expressing high levels of P-450g (+g) and those expressing low levels of P-450g (-g). The P-450g content of the two populations differed 10- to 20-fold. P-450g was low or absent in liver microsomes of both sexes of adult Fischer rats. Purified P-450g catalyzed the hydroxylation of testosterone and androstenedione principally at the 6 beta-position and progesterone at the 16 alpha- and 6 beta-positions in reconstituted systems. However, the hydroxylation of these steroids by liver microsomes from the (+g) phenotype did not differ from that of the (-g) phenotype. Translatable mRNA for P-450g could be detected in livers of adult male CD rats but not female rats. However, the level of P-450g mRNA in livers of adult male CD rats with the (+g) phenotype did not differ from that of (-g) phenotype. These data suggest that phenotypic differences in the expression of P-450g do not depend on differences in mRNA content. This study provides a clear example of a P-450 isozyme which is markedly variable in an outbred strain of rat and absent in an inbred strain. Such a marked variability in an enzyme involved in metabolism of endogenous and exogenous substrates could account for some of the strain differences in susceptibility to toxic chemicals.
D000735:Androstenedione / Q000378:metabolism; D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D005260:Female; D005786:Gene Expression Regulation; D014644:Genetic Variation; D007163:Immunosorbent Techniques; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D010641:Phenotype; D011374:Progesterone / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D012737:Sex Factors; D012741:Sexual Maturation; D013250:Steroid Hydroxylases / Q000235:genetics / Q000378:metabolism; D013739:Testosterone / Q000378:metabolism
D012333:RNA, Messenger; D013739:Testosterone; D000735:Androstenedione; D011374:Progesterone; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases