Molecular turnover numbers of different forms of mitochondrial monoamine oxidase in rat

Molecular turnover numbers of the different forms of monoamine oxidase in rat liver were estimated for serotonin, tyramine and beta-phenylethylamine by titration with irreversible inhibitors. The 'A' form was found to have a much higher turnover number for serotonin and a lower turnover number for beta-phenylethylamine than the 'B' form, while the turnover numbers for tyramine were in the same order of magnitude for both forms. The monoamine oxidase in the liver was found to have a significantly higher molecular turnover for tyramine and beta-phenylethylamine than that in the brain, heart and kidney. It was calculated that the 'A' form of monoamine oxidase amounted to about 20% and the 'B' form to about 80% of the total amount of monoamine oxidase in the rat liver mitochondrial preparation. The number of molecules per mitochondrion was also calculated.