The Journal of Biochemistry
Online ISSN : 1756-2651
Print ISSN : 0021-924X
Tyrosine Residues near the FAD Binding Site Are Critical for FAD Binding and for the Maintenance of the Stable and Active Conformation of Rat Monoamine Oxidase A
Jichun MaAkio Ito
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2002 Volume 131 Issue 1 Pages 107-111

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Abstract

Monoamine oxidase is a flavin-containing enzyme which is located at the mitochondrial outer membrane and catalyzes the oxidative deamination of amines. To investigate the role of tyrosine residues near the FAD-binding site, Cys-406, of monoamine oxidase A, the tyrosine residues at positions 402, 407, and 410 were individually replaced with alanine or phenylalanine and the effects of the mutations on catalytic activity, FAD binding, and enzyme structure were examined. Half or fewer of the mutant proteins incorporated FAD. The mutation of Tyr-407 to alanine led to an almost completely loss of catalytic activity for serotonin, phenylethylamine, tyramine, and tryptamine. A substantial decrease in the catalytic activity was also observed with the enzymes mutated at Tyr-402 and Tyr-410 to alanine, although the effect of the latter mutation was much less. All these mutants were sensitive to trypsin treatment of the purified enzyme, while the wild type enzyme was resistant to treatment. On the other hand, substitution of Tyr-402 or Tyr-407 with phenylalanine had little effect on these properties. Taken together, we conclude that tyrosine residues near Cys-406 may form a pocket to facilitate FAD incorporation, the catalytic center, and a stable conformation, probably through interactions among the aromatic rings of the tyrosine residues and FAD.

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© The Japanese Biochemical Society
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