Arginyl Residues of Adrenodoxin Reductase as the Anion Recognition Site for 2′-Phosphate Group of NADP+1

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Abstract
Adrenodoxin reductase from bovine adrenocortex was inactivated by arginine specific reagents, p-hydroxyphenylglyoxal, phenylglyoxal, 2,3-butanedione, and 1,2-cyclohexanedione. Inactivation of the enzyme caused by p-hydroxyphenylglyoxal obeyed pseudo-first-order kinetics and resulted in complete elimination of NADPH-ferricyanide reductase activity. The rate of inactivation increased with pH from 6.5 to 9.5. Ten out of 30–33 arginyl residues of the enzyme were modified, but residues essential to its enzymatic activity were less than 5. NADP+ strongly protected against inactivation by p-hydroxyphenylglyoxal, whereas NADP+ could afford only partial, weak protection. Furthermore, 2′-AMP and 2′,5′-ADP afforded considerable protection but 5′-AMP did not. These data suggest that adrenodoxin reductase has essential arginyl residues which are crucial to the enzymatic activity as the recognition site for the negatively charged 2′-phosphate group of NADP+.

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