Inhibition of aldosterone production in rat adrenal mitochondria by 18-ethynyl-11-deoxycorticosterone: A simple model for kinetic interpretation of mechanism-based inhibitors
A simple mathematical model for studying mechanism-based inhibitors (MBIs) is presented. The mathematical equations are deduced for an experimental protocol consisting of a first incubation of the enzyme in the presence of MBI followed by a washing protocol to eliminate free MBI. Finally enzyme acti...
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2001
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| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_0021924X_v129_n3_p383_Matkovic http://hdl.handle.net/20.500.12110/paper_0021924X_v129_n3_p383_Matkovic |
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| Sumario: | A simple mathematical model for studying mechanism-based inhibitors (MBIs) is presented. The mathematical equations are deduced for an experimental protocol consisting of a first incubation of the enzyme in the presence of MBI followed by a washing protocol to eliminate free MBI. Finally enzyme activity (initial velocity) is measured with specific substrate. The representation of the final equation obtained is a straight line, and the MBI-specific association constant of velocity (k) can be calculated from its slope. The mathematical model was then challenged with the effect of 18-ethynyl-11-deoxycorticosterone (18-EtDOC) as an MBI on aldosterone biosynthesis from 11-deoxycorticosterone (DOC) in rat adrenal mitochondria. The last step of the mitochondrial biosynthesis of aldosterone consists of the conversion of DOC into corticosterone (B) or 18-hydroxy-11-deoxycorticosterone (18-OHDOC), and both steroids can then be transformed into aldosterone. The k (mM-1·min-1) values obtained for 18-EtDOC were: 451 ± 36 for DOC to aldosterone; 177 ± 16 for B to aldosterone; 175 ± 15 for 18-OHDOC to aldosterone; and 2.7 ± 0.2 for DOC to B. These results show that this MBI practically does not affect the metabolism of DOC to B in our enzyme preparation and that conversions of B and 18-OHDOC into aldosterone are catalyzed by the same enzyme. |
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