title: Seasonal changes in the activity of cytochrome P450(C17) from the testis of Bufo arenarum.
abstract: In Bufo arenarum, the biosynthesis of testosterone and 5alpha-dihydrotestosterone takes place through a complete 5-ene pathway, 5-androsten-3beta,17beta-diol being the immediate precursor of testosterone. Besides androgens, testes are able to synthesise 5alpha-pregnan-3,20-dione and several 3alpha and 20alpha reduced derivatives. During the breeding season, steroid biosynthesis turns from androgen to C21-steroid production. As a consequence, the cytochrome P450 17-hydroxylase, C17,20-lyase (CypP450(c17)) could be a key enzyme in that metabolic shift. The present study demonstrates that in testes of B. arenarum, CypP450(c17) co-localises with glucose-6-phosphatase in the microsomal fraction. CypP450(c17) possesses more affinity for pregnenolone than for progesterone in both non-reproductive (Km = 43.76 +/- 4.63 nM and 2,170 +/- 630 nM, respectively) and reproductive (Km = 37.46 +/- 4.19 nM and 3,060 +/- 190 nM, respectively) seasons. These results could explain the predominance of the 5-ene pathway for testosterone biosynthesis. Toad CypP450(c17) activity is higher in the non-reproductive period than the reproductive period, suggesting that this enzyme is an important factor in toad steroidogenic changes. Animals in reproductive conditions showed a significant reduction in circulating androgens. This is in agreement with the decrease in Vmax of cytochrome P450 17-hydroxylase activity, enhancing the physiological relevance of these in vitro results.
authors.affiliation: PRHOM-CONICET and Laboratorio de Endocrinología Comparada, Departamento de Biodiversidad y Biología Experimental, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: J J F
authors.initials: JJ
authors.lastname: Solari
authors.forename: A G
authors.initials: AG
authors.lastname: Pozzi
authors.forename: N R
authors.initials: NR
authors.lastname: Ceballos
mesh_terms: D000818:Animals; D002022:Bufo arenarum / Q000378:metabolism*; D007106:Immune Sera; D007700:Kinetics; D008297:Male; D012621:Seasons; D013254:Steroid 17-alpha-Hydroxylase / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism; D013737:Testis / Q000378:metabolism*; D013739:Testosterone / Q000097:blood; D014018:Tissue Distribution
chemical_list: D007106:Immune Sera; D013739:Testosterone; D013254:Steroid 17-alpha-Hydroxylase