Stereospecificity in the metabolism of aldosterone in man.
نویسنده
چکیده
Although stereospecificity is characteristic of the reactions of single enzymes, both optical antipodes are usually metabolized in a qualitatively similar manner in the intact animal (l-4) where numerous possibilities of enzyme attack exist. When dl-aldosterone and other racemic steroids are added to enzyme or microbial systems (5, 6), only the naturally occurring d antipodes undergo reaction, whereas the 1 isomers are recovered unchanged. The fate of the 1 steroids in vivo, however, is not known. Since aldosterone has been available chiefly in racemic form,’ the metabolism of its I antipode was of interest. In the present study, a method for comparing the metabolism of a pair of antipodes has been applied to measure the conversion of I-aldosterone to each of the two known urinary products of the d isomer in man, the conjugate which is hydrolyzed at pH 1 (10) and tetrahydroaldosterone2 (11). The method consisted of administering a known mixture of dand dl-aldosterone and comparing the ratio of d to dl forms in the administered mixture with that found in the urinary metabolites. Two methods were used to measure the ratio of d-aldosterone to dl-aldosterone. 1. When the endogenous production of aldosterone was negligible, the d isomer was administered in labeled form and racemic aldosterone in unlabeled form. The ratio of dto racemic aldosterone was determined from the specific activity. 2. Alternatively, dand racemic aldosterone were each labeled with different isotopes, H3 and CY4. The ratio of dto racemic aldosterone was determined from the ratio of H3 to Cl*. Both methods demonstrated that over-all metabolism of aldosterone in man is stereospecific. Z-Aldosterone was not converted either to the conjugate hydrolyzed at pH 1 or to tetrahydroaldosterone.
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عنوان ژورنال:
- The Journal of biological chemistry
دوره 236 شماره
صفحات -
تاریخ انتشار 1961