scholarly journals Carbethoxylation and pH profiles of kinetic parameters of 20.BETA.-hydroxysteroid dehydrogenase from Streptomyces hydrogenans.

1982 ◽  
Vol 30 (8) ◽  
pp. 2874-2879 ◽  
Author(s):  
TSUYOSHI TANIMOTO ◽  
TAKAO HAYAKAWA ◽  
HIDEO FUKUDA ◽  
JIRO KAWAMURA
Keyword(s):  
Kinetic Parameters ◽  
Hydroxysteroid Dehydrogenase ◽  
Ph Profiles

THE INFLUENCE OF ETHANOL ON THE CONVERSION OF PREGNENOLONE TO PROGESTERONE BY HUMAN PLACENTAL MICROSOMES

1974 ◽  
Vol 76 (1) ◽  
pp. 178-188 ◽  
Author(s):  
H. Lübbert ◽  
K. Pollow ◽  
R. Wagner ◽  
J. Hammerstein
Keyword(s):  
Kinetic Parameters ◽  
Enzyme Preparation ◽  
Ethanol Concentration ◽  
Hydroxysteroid Dehydrogenase ◽  
Product Formation ◽  
Linear Increase ◽  
Maximal Velocity ◽  
Microsomal Enzyme ◽  
Temperature Optima ◽  
Substrate Concentrations

ABSTRACT The effects of ethanol on kinetic parameters of placental Δ5-3β-hydroxysteroid dehydrogenase were studied. In the presence of high pregnenolone concentrations (50 μm, [S] > Km) the microsomal enzyme preparation exhibited an almost linear increase in activity as the ethanol concentration in the medium was raised from 2.5 to 15 % (v/v). At lower substrate concentrations ([S] << Km) ethanol caused inhibition. Other effects of ethanol were: linearity of product formation with time was prolonged; the maximal velocity was markedly increased; the Km for pregnenolone slightly decreased with increasing ethanol concentrations (2.5 to 10 %, v/v) whereas the Km for NAD remained the same. The pH and temperature optima of the reaction were unaffected by ethanol. Other organic solvents caused similar effects.

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

1984 ◽  
Vol 4 (6) ◽  
pp. 483-488 ◽  
Author(s):  
Nikolaus Kühn-Velten ◽  
Joachim Wolff ◽  
Wolfgang Staib
Keyword(s):  
Steady State ◽  
Kinetic Parameters ◽  
Active Site ◽  
Enzyme Activities ◽  
Substrate Concentration ◽  
Leydig Cells ◽  
Hydroxysteroid Dehydrogenase ◽  
Endogenous Substrate ◽  
Catalyzed Reactions ◽  
Actual Substrate

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.

Kinetic comparison of the 3β-hydroxysteroid dehydrogenase activity in human placenta, chorion laeve, and ovary

1985 ◽  
Vol 63 (3) ◽  
pp. 183-186 ◽  
Author(s):  
W. Gibb ◽  
J. C. Lavoie ◽  
M. Morin-Gonthier
Keyword(s):  
Kinetic Parameters ◽  
Dehydrogenase Activity ◽  
Human Placenta ◽  
Hydroxysteroid Dehydrogenase ◽  
The Other ◽  
Human Tissues ◽  
Other Hand ◽  
Chorion Laeve ◽  
Human Ovaries ◽  
Nanomolar Range

Recent studies from our laboratory and others have shown that Km values for steroid substrates of the 3β-hydroxysteroid dehydrogenase in the human placenta were in the nanomolar range compared with micromolar values previously described. The purpose of the present study was to measure the kinetic parameters of the 3β -hydroxysteroid dehydrogenase in other human tissues, namely the ovary and chorion laeve, and to determine whether they were similar to those of the placental enzyme. In chorion laeve microsomes the 3β-hydroxysteroid dehydrogenase had Km values for dehydroepiandrosterone and pregnenolone similar to those found in placenta. Microsomes from human ovaries, on the other hand, had Km values for both substrates 10- to 20-fold higher. However, the ability of various steroids to inhibit the ovarian enzyme was similar to that previously described from the placenta and the chorion laeve.

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