Multiple Forms of Monoamine Oxidase in Developing Tissues: The Implications for Mental Disorder
For a number of years our laboratory has been concerned with the developmental characteristics of the biogenic amines in the maturing brain (Eiduson 1966; Eberle and Eiduson 1968). More specifically, we believe as others do that a knowledge of how the biosynthesis, tissue levels, and catabolism of these amines are regulated during brain development may lead to a greater understanding of the biochemical and behavioral individuality exhibited by higher organisms and man himself. Little knowledge has been adduced about these regulatory mechanisms, especially during the formative period of development, although some workers have suggested end-product feed-back inhibition in the case of norepinephrine biosynthesis (Spector et al. 1967), or end-product feed-back repression of the enzyme involved in the first step of serotonin biosynthesis (Eiduson 1966). Thus we have been led to speculate about the possible mechanisms that may play a role in the regulation of these amines in different parts of the brain, and especially during development of the brain. These considerations, as well as our search and interpretation of the literature, have led us to consider the notion that there may exist multiple forms (isoenzymes) of monoamine oxidase (monoamine: O2-oxidoreductase [deaminating] EC 18.104.22.168) that may play a significant role in the regulation of these important neurohumoral substances. We shall be using the terms “multiple forms” of an enzyme and “isoenzyme” interchangeably since it is difficult to give a very precise definition of the word “isoenzyme.” We shall accept as definition for the time being, as was suggested by Latner and Skillen (1968), that “...most authorities believe that a broad definition such as ‘different proteins with similar enzymatic activity’ best suits the current state of our knowledge. It is customary, for the most part, to limit this definition to multiple enzymes obtained from one tissue of one individual animal or plant or possibly a small organ, or a culture of a unicellular organism.” Accordingly, the properties of monoamine oxidase (MAO) and especially its activity in developing brain (and other tissues of the maturing organism), as well as in certain clinical disease entities, serve as the subject matter of this paper.
KeywordsMonoamine Oxidase Multiple Form Amine Oxidase Develop Brain Diagrammatic Sketch
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