Multiple Forms of Monoamine Oxidase in Developing Brain: Tissue and Substrate Specificities

Brains, hearts and livers from newborn and adult rats were assayed for monoamine oxidase activity using gel electrophoretic techniques. The results suggest that each of the tissues possesses multiple forms (isoenzymes) of monoamine oxidase and that these forms are different for the various tissues. Further, the forms of monoamine oxidase in the neonatal tissues differ from those in the corresponding adult tissue. These different forms of monoamine oxidase have different substrate specificities. Using 5‐hydroxy[ 14 C]tryptamine as substrate, we have demonstrated that the monoamine oxidase patterns appearing on the gel do indeed possess monoamine oxidase activity.