Inactivation of myoglobin by ortho-substituted arylhydrazines. Formation of prosthetic heme aryl-iron but not N-aryl adducts.

Stable phenyl-iron complexes are known to form in the reactions of myoglobin, hemoglobin, and catalase with phenylhydrazine. The phenyl moiety in these complexes migrates from the iron to a nitrogen of the porphyrin upon denaturation of the hemoproteins. Complexes obtained from myoglobin and ortho-substituted phenylhydrazines, however, are much less stable, have distinct chromophores, and do not yield N-arylporphyrins. These abnormal properties imply that the complexes differ in structure (e.g., they are aryldiazenyl-rather than aryl-iron complexes) or that ortho substitution strongly alters the chemistry of aryl-iron complexes. The present NMR studies unambiguously demonstrate that ortho-substituted phenylhydrazines give normal aryl-iron complexes but that the aryl group in these complexes is conformationally locked and is unable to shift from iron to nitrogen.