Subcellular metabolic pools in the rat adrenal gland. in vivo effect of acute stimulation with ACTH on steroid biosynthesis

Herrera, J; León, C. Inés; Morán, L.Z.; Raudales, Leticia; Bermúdez, José

doi:10.1016/0022-4731(80)90186-7

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Cited by 8 publications

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Estimation of kinetic parameters of androgen-synthesizing enzyme activities in superfused Leydig cells from rat testes: Difference between endogenous and exogenous substrates

1984

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Kinetic parameters of 3 beta-hydroxysteroid dehydrogenase/isomerase, steroid-17 alpha-monooxygenase, and steroid-17,20-lyase activities were estimated under steady-state conditions. Purified Leydig cells from rat testes were superfused with pregnenolone, progesterone, or 17 alpha-hydroxyprogesterone. The Km values for both the monooxygenase- and the lyase-catalyzed reactions were by factors of five to ten higher if analyzed with the exogenously added substrate (0.98 and 0.65 microM, respectively) than if calculated from endogenous substrate derived from a precursor (0.10 and 0.13 microM, respectively). This discrepancy may be explained by different substrate partition between the intra- and extracellular spaces and by different substrate concentration at the active site of the respective enzyme, depending on whether the actual substrate is of exogenous or endogenous source.

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