Kinetic properties of microsomal 3β hydroxysteroid dehydrogenase-isomerase from the testis of Bufo arenarum H

3β-hydroxysteroid dehydrogenase 5-ene isomerase (3βHSD/I) activity is necessary for the biosynthesis of hormonally active steroids. A dual distribution of the enzyme was described in toad testes. The present study demonstrates that in testicular tissue of Bufo arenarum H., microsomal 3βHSD/I has mor...

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Detalles Bibliográficos
Publicado: 2000
Materias:
3HSD/I
Non-competitive inhibition
Steroid biosynthesis
Toad-testis
3(or 17)beta hydroxysteroid dehydrogenase
androstenedione
carbon 14
microsome enzyme
prasterone
pregnenolone
progesterone
steroid hormone
tritium
animal tissue
article
binding site
biosynthesis
enzyme assay
enzyme kinetics
male
microsome
nonhuman
steroid metabolism
steroidogenesis
testis
thin layer chromatography
toad
Acceso en línea:https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_09600760_v73_n5_p257_Pozzi
http://hdl.handle.net/20.500.12110/paper_09600760_v73_n5_p257_Pozzi
Aporte de:
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
id paper:paper_09600760_v73_n5_p257_Pozzi
record_format dspace
spelling paper:paper_09600760_v73_n5_p257_Pozzi2023-06-08T15:57:26Z Kinetic properties of microsomal 3β hydroxysteroid dehydrogenase-isomerase from the testis of Bufo arenarum H 3HSD/I Non-competitive inhibition Steroid biosynthesis Toad-testis 3(or 17)beta hydroxysteroid dehydrogenase androstenedione carbon 14 microsome enzyme prasterone pregnenolone progesterone steroid hormone tritium animal tissue article binding site biosynthesis enzyme assay enzyme kinetics male microsome nonhuman steroid metabolism steroidogenesis testis thin layer chromatography toad 3β-hydroxysteroid dehydrogenase 5-ene isomerase (3βHSD/I) activity is necessary for the biosynthesis of hormonally active steroids. A dual distribution of the enzyme was described in toad testes. The present study demonstrates that in testicular tissue of Bufo arenarum H., microsomal 3βHSD/I has more affinity for dehydroepiandrosterone (DHEA) than for pregnenolone (K(m) = 0.17 ± 0.03 and 1.02 μM, respectively). The Hill coefficient for the conversion of DHEA and pregnenolone were 1.04 and 1.01, respectively. The inclusion of DHEA in the kinetic analysis of pregnenolone conversion affected V(max) while K(m) was not modified, suggesting a non-competitive inhibition of the conversion of pregnenolone. K(i) was calculated from replot of Dixon's slope for each substrate concentration. K(i) from the intercept and the slope of this replot were similar (0.276 ± 0.01 and 0.263 ± 0.02 μM) and higher than the K(m) for DHEA. The K(m) and K(i) values suggest the presence of two different binding sites. When pregnenolone was present in the assays with DHEA as substrate, no effect was observed on the V(max) while K(m) values slightly increased with pregnenolone concentration. Consequently, pregnenolone inhibited the transformation of DHEA in a competitive fashion. These studies suggest that, in this species, the microsomal biosyntheses of androgens and progesterone are catalysed by different active sites. (C) 2000 Elsevier Science Ltd. 2000 https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_09600760_v73_n5_p257_Pozzi http://hdl.handle.net/20.500.12110/paper_09600760_v73_n5_p257_Pozzi
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
topic 3HSD/I
Non-competitive inhibition
Steroid biosynthesis
Toad-testis
3(or 17)beta hydroxysteroid dehydrogenase
androstenedione
carbon 14
microsome enzyme
prasterone
pregnenolone
progesterone
steroid hormone
tritium
animal tissue
article
binding site
biosynthesis
enzyme assay
enzyme kinetics
male
microsome
nonhuman
steroid metabolism
steroidogenesis
testis
thin layer chromatography
toad
spellingShingle 3HSD/I
Non-competitive inhibition
Steroid biosynthesis
Toad-testis
3(or 17)beta hydroxysteroid dehydrogenase
androstenedione
carbon 14
microsome enzyme
prasterone
pregnenolone
progesterone
steroid hormone
tritium
animal tissue
article
binding site
biosynthesis
enzyme assay
enzyme kinetics
male
microsome
nonhuman
steroid metabolism
steroidogenesis
testis
thin layer chromatography
toad
Kinetic properties of microsomal 3β hydroxysteroid dehydrogenase-isomerase from the testis of Bufo arenarum H
topic_facet 3HSD/I
Non-competitive inhibition
Steroid biosynthesis
Toad-testis
3(or 17)beta hydroxysteroid dehydrogenase
androstenedione
carbon 14
microsome enzyme
prasterone
pregnenolone
progesterone
steroid hormone
tritium
animal tissue
article
binding site
biosynthesis
enzyme assay
enzyme kinetics
male
microsome
nonhuman
steroid metabolism
steroidogenesis
testis
thin layer chromatography
toad
description 3β-hydroxysteroid dehydrogenase 5-ene isomerase (3βHSD/I) activity is necessary for the biosynthesis of hormonally active steroids. A dual distribution of the enzyme was described in toad testes. The present study demonstrates that in testicular tissue of Bufo arenarum H., microsomal 3βHSD/I has more affinity for dehydroepiandrosterone (DHEA) than for pregnenolone (K(m) = 0.17 ± 0.03 and 1.02 μM, respectively). The Hill coefficient for the conversion of DHEA and pregnenolone were 1.04 and 1.01, respectively. The inclusion of DHEA in the kinetic analysis of pregnenolone conversion affected V(max) while K(m) was not modified, suggesting a non-competitive inhibition of the conversion of pregnenolone. K(i) was calculated from replot of Dixon's slope for each substrate concentration. K(i) from the intercept and the slope of this replot were similar (0.276 ± 0.01 and 0.263 ± 0.02 μM) and higher than the K(m) for DHEA. The K(m) and K(i) values suggest the presence of two different binding sites. When pregnenolone was present in the assays with DHEA as substrate, no effect was observed on the V(max) while K(m) values slightly increased with pregnenolone concentration. Consequently, pregnenolone inhibited the transformation of DHEA in a competitive fashion. These studies suggest that, in this species, the microsomal biosyntheses of androgens and progesterone are catalysed by different active sites. (C) 2000 Elsevier Science Ltd.
title Kinetic properties of microsomal 3β hydroxysteroid dehydrogenase-isomerase from the testis of Bufo arenarum H
title_short Kinetic properties of microsomal 3β hydroxysteroid dehydrogenase-isomerase from the testis of Bufo arenarum H
title_full Kinetic properties of microsomal 3β hydroxysteroid dehydrogenase-isomerase from the testis of Bufo arenarum H
title_fullStr Kinetic properties of microsomal 3β hydroxysteroid dehydrogenase-isomerase from the testis of Bufo arenarum H
title_full_unstemmed Kinetic properties of microsomal 3β hydroxysteroid dehydrogenase-isomerase from the testis of Bufo arenarum H
title_sort kinetic properties of microsomal 3β hydroxysteroid dehydrogenase-isomerase from the testis of bufo arenarum h
publishDate 2000
url https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_09600760_v73_n5_p257_Pozzi
http://hdl.handle.net/20.500.12110/paper_09600760_v73_n5_p257_Pozzi
_version_ 1768546125295386624

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