Potassium intake and aldosterone biosynthesis: the role of cytochrome P-450

K+ Repletion for 48 h of rats previously kept on a low K+ diet for 2 weeks specifically increased the conversion of corticosterone into aldosterone and 18-hydroxycorticosterone by incubated capsular fractions of rat adrenal tissue. This increase in the activity of the final steps of aldosterone biosynthesis was not accompanied by an increase in capsular adrenal mitochondrial cytochrome P-450 concentration. By contrast, an increased corticosterone-induced absorbance change (BI) was consistently found in capsular adrenal mitochondria upon K+ repletion. In addition, a type I-like absorbance change was induced with 18-hydroxy-11-deoxycorticosterone but not with 18-hydroxycorticosterone. Therefore, K+ repletion of K+ depleted rats specifically increased the binding of corticosterone and possibly 18-hydroxy-11-deoxycorticosterone to the 18-methyl oxidase enzyme complex. Whether this increased binding was due to an increase in enzyme protein concentration or due to a better availability of the substrate to the enzyme, could not be decided from these experiments.