Figure 5.

Reduction of MAO A by methylene blue (MB) in the presence of D-amphetamine and dithiothreitol (DTT). MAO A was diluted eightfold from stock to 27 μM so that the concentration of D-amphetamine was 60 μM and of DTT about 0.35 mM, was made anaerobic, and 30 μM MB added both to the MAO A cuvette and to the blank cuvette. The spectral change after the addition showed some reduction of MB (decrease at 665 nm) and appearance of the features of the MAO A anionic semiquinone (increase at 380 and 412 nm, decrease at 456 nm). After 2 h at 20°C, the spectrum indicated almost complete conversion of MAO A to the semiquinone form. No further change was observed even 24 h later.