Abstract
The adrenal microsomal sediment of domestic duck ( Anas platyrhynchos) contains an enzyme system which hydroxylates exogenous progesterone or 17α-hydroxyprogesterone to 11-deoxy-corticosterone or to 11-deoxycortisol respectively. This system required atmospheric oxygen and reduced NADP. The microsomal 21-hydroxylase had a micromolar Michaelis-Menten constant, at saturation conditions produced 11.67 nmoles of 11-deoxycorticosterone/mg of microsomal protein/min and only the above two steroids were accepted as substrates. Optimal temperature for the 21-hydroxylase was 37°C (Q 10:1.4). The system required 2–3 moles of NADPH/moles of substrate for maximal activity. Carbon monoxyde, mctopirone, cytochrome c and p-chloromercuribenzoate inhibited partially the microsomal 21-hydroxylation. The spectrophotometric presence of cytochrome P-450 could be demonstrated. Progesterone, 17α-hydroxyprogesterone and metopirone induced type I (maximum at 406 nm and minimum at 420 nm) difference spectra. It is suggested that the duck adrenal microsomal 21-hydroxylase might differ in stoichiometry and substrate specificity from equivalent mammalian preparations.
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