Studies on Adrenal Steroid Hydroxylases

Treatment of adrenal iron-sulfur protein (adrenodoxin) with urea and guanidine HCl results in a deterioration reaction that proceeds through at least two intermediate stages yielding the completely denaturated, colorless protein. The first transient state exhibits a circular dichroism maximum at 470 mµ which is shifted to a longer wave length than that of the native protein (440 mµ); at 470 mµ it has a much smaller ellipticity than the original protein at 440 mµ. The absorption spectrum of this first intermediate is almost identical with the native protein. The second transient state displays no Cotton effect and the optical absorption spectrum is similar to the native protein; the extinction coefficient at 414 mµ is about half that of the untreated protein. The deterioration process of spinach ferredoxin in the presence of urea and guanidine HCl resembles that of adrenal iron-sulfur protein. The reaction also proceeds through an intermediate state, giving rise to a circular dichroism maximum at 470 mµ. The results show that different kinetic profiles of optical activity and optical absorption are involved in the deterioration process of the chromophore in iron-sulfur proteins.