AUotopic Properties of Human Brain Monoamine Oxidase

Abstract

A NUMBER of preparations of monoamine oxidase (monoamine: O₂ oxidoreductase (deaminating) E.C.1.4.3.4.) (MAO) have been shown to contain multiple forms of the enzyme which differ in their electrophoretic mobilities^{1, 2}, inhibitor sensitivities^3–5, thermal stabilities⁶ and, in some cases, immunological properties^7–8. Little is known about the nature of these multiple forms although it has been suggested that they might be protein conformers⁹. The possibility that they might arise from the binding of different amounts or types of lipid material to a single enzyme species is, however, supported by the observation that the electrophoretically separable forms of rat liver MAO contain widely different amounts of phospholipid^{5, 10}. In addition we have recently shown that treatment of a preparation of rat liver monoamine oxidase with the chaotropic agent sodium perchiorate seemed to render the enzyme homogeneous by a number of criteria without any significant loss of activity¹⁰. This treatment was shown to be accompanied by the release of lipid material from the enzyme preparation and, since chaotropic agents are known to weaken hydrophobic bonds between protein and lipid¹¹, these results gave further support to the view that the multiple forms are caused by the association of lipid membrane material with a single enzyme.