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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

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Bioscience Reports

Abstract

Kinetic parameters of 3β-hydroxysteroid dehydrogenase/isomerase, steroid-17α-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 17α-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 μM, respectively) than i f calculated from endogenous substrate derived from a precursor (0.10 and 0.13 μM, respectively). This discrepancy may be explained by different substrate partition between the intra- and extraceIJular 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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Authors and Affiliations

  1. Institut für Physiologische Chemie II, Universität, Moorenstrasse 5, D-4000, Dusseldorf, Germany

    Nikolaus Kühn-Velten, Joachim Wolff & Wolfgang Staib

Authors
  1. Nikolaus Kühn-Velten
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  2. Joachim Wolff
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  3. Wolfgang Staib
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Kühn-Velten, N., Wolff, J. & Staib, W. Estimation of kinetic parameters of androgen-synthesizing enzyme activities in superfused Leydig cells from rat testes: Difference between endogenous and exogenous substrates. Biosci Rep 4, 483–488 (1984). https://doi.org/10.1007/BF01122223

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  • DOI: https://doi.org/10.1007/BF01122223

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