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 if 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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June 01 1984
Estimation of kinetic parameters of androgen-synthesizing enzyme activities in superfused Leydig cells from rat testes: Difference between endogenous and exogenous substrates
Nikolaus Kühn-Velten;
Nikolaus Kühn-Velten
1Institut für Physiologische Chemie II, Universität, Moorenstrasse 5, D-4000 Dusseldorf, Germany
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Joachim Wolff;
Joachim Wolff
1Institut für Physiologische Chemie II, Universität, Moorenstrasse 5, D-4000 Dusseldorf, Germany
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Wolfgang Staib
Wolfgang Staib
1Institut für Physiologische Chemie II, Universität, Moorenstrasse 5, D-4000 Dusseldorf, Germany
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Publisher: Portland Press Ltd
Received:
April 24 1984
Online ISSN: 1573-4935
Print ISSN: 0144-8463
© 1984 The Biochemical Society
1984
Biosci Rep (1984) 4 (6): 483–488.
Article history
Received:
April 24 1984
Citation
Nikolaus Kühn-Velten, Joachim Wolff, Wolfgang Staib; Estimation of kinetic parameters of androgen-synthesizing enzyme activities in superfused Leydig cells from rat testes: Difference between endogenous and exogenous substrates. Biosci Rep 1 June 1984; 4 (6): 483–488. doi: https://doi.org/10.1007/BF01122223
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