Spectrometric evidence for the flavin-1-phenylcyclopropylamine inactivatoradduct with monoamine oxidase N

1-Phenylcycloplopylamine (1-PCPA) is shown to be an inactivator of the fung al flavoenzyme monoamine oxidase (MAO) N. inactivation results in an increa se in absorbance at 410 nm and is accompanied by the concomitant loss of th e flavin absorption band at 458 nm. The spectral properties of the covalent adduct formed between the flavin cofactor of MAO N and I-PCPA are similar to those reported for the irreversible inactivation product formed with 1-P CPA and mammalian mitochondrial monoamine oxidase B [Silverman, R. B., and Zieske, P. A. (1985) Biochemistry 24, 2128-2138]. There is a hypsochromic s hift of the 410 nm band upon lowering the pH to 2, indicating that an N-5-f lavin adduct formed upon inactivation. Use of the fungal enzyme, MAO N, whi ch lacks the covalent attachment to the flavin adenine dinucleotide (FAD) c ofactor present in the mammalian forms MAO A and MAO B, has allowed for the isolation and further structural identification of the flavin-inactivator adduct. The incorporation of two C-13 labels into the inactivator, [2,3-C-1 3(2)]-1-PCPA, followed by analysis using online liquid chromatography/elect rospray ionization mass spectrometry and nuclear magnetic resonance spectro scopy, provided a means to explore the structure of the flavin-inactivator adduct of MAO N. The spectral evidence supports covalent attachment of the 1-PCPA inactivator to the cofactor as N-5-3-oxo-3-phenylpropyl-FAD.