Type-B Monoamine Oxidase

By Joseph Knoll

Type-B monoamine oxidase (MAO-B) is the form of monoamine oxidase (MAO) that is insensitive to clorgyline. Clorgyline, 3-(2, 4-dichlorophenoxy)-N-methyl-N-2-ynylpropan-1-amine, is an irreversible MAO-inhibitor substance, structurally related to pargyline. The term was coined and introduced, in 1968, by Johnston, to distinguish between clorgyline-sensitive and insensitive forms of monoamine oxidase (MAO) enzymes, referred to as Type-A monoamine oxidase and Type-B monoamine oxidase, respectively. MAO-B was found to be present in the neurons, astroglia and platelets (Neff and Gorodis 1972) and was primarily responsible for the oxidative deamination of beta-phenylethylamine and benzylamine (Costa and Sandler 1972). In 1971, it was shown that MAO activity progressively increased in the aging brain (Robinson et al. 1971) and, by 1980, it was also recognized that this was due entirely to the increase in MAO-B concentrations in brain tissue (Fowler et al. 1980).  The first selective MAO-B inhibitor, (-)-deprenyl/selegiline, an (R) –N- methyl-N-(1-phenylpropan-2-yl) prop-2-yn-1-amine, was identified, in1972, by Knoll and Magyar.

Costa E, Sandler M (editors). Monoamine Oxidases – New Vistas. Advances in Biochemical Psychopharmacology. Volume 5. New York:  Raven Press; 1972.

Fowler CJ, Wiberg A, Oreland L, Marcusson J, Winblad B. The effect of age on the activity and molecular properties of human brain monoamine oxidase. Journal Neural Transmission 1980; 49:1-20.

Johnston JP. Some observations upon a new inhibitor of monoamine oxidase in human brain. Biochemical Pharmacology 1968; 17:1285-97.

Knoll J, Magyar K. Some puzzling pharmacological effects of monoamine oxidase inhibitors. Adv Biochem Psychoharmacol 1972; 5: 393-408.

Robinson DS, Davis JM, Nies A, Ravaris C.L, Sylwester D. Relation of sex and aging to monoamine oxidase activity in human brain, plasma and platelets. Archives General Psychiatry 1971; 24:536-9.

Joseph Knoll
August 28, 2014