The characterization of monoamine oxidase in cultured mammalian cells

— The expression of monoamine oxidase (MAO) in a variety of mammalian cells has been investigated employing tryptamine as substrate. The enzyme present in those cell lines having sufficient activity for detailed analysis exhibited a monophasic response to the inhibitor clorgyline. On this basis the cell lines examined were found to express only A, or only B, type activity. Hypoxanthineguanine phosphoribosyl transferase (HGPRT) deficient derivatives of both MAO type A, or MAOtype B, expressing cells were examined. The HGPRT status of the cells appeared to have little influence on the expression of the enzyme.