Nervous tissue substrate specificity

Since the brain expresses many mRNAs that are also found in non-nervous tissue and are therefore of little interest to the psychopharmacologist, it is necessary to isolate only those cDNAs that, for example, encode for a specific enzyme or receptor protein. Several techniques have been developed to achieve this. For example, a specific cDNA plasmid may be inserted into cultured mammalian cells such as fibroblasts that can express the specific receptor or enzyme. Once this has been expressed in the culture medium, the receptor or enzyme can be identified by adding a specific ligand or substrate. This enables those cells that expressed the specific macromolecule of interest to be identified and... 

Amine oxidation. As well as the microsomal enzymes involved in the oxidation of amines, there are a number of other amine oxidase enzymes, which have a different subcellular distribution. The most important are the monoamine oxidases and the diamine oxidases. The monoamine oxidases are located in the mitochondria within the cell and are found in the liver and also other organs such as the heart and central nervous system and in vascular tissue. They are a group of flavoprotein enzymes with overlapping substrate specificities. Although primarily of importance in the metabolism of endogenous compounds such as 5-hydroxy try pt-amine, they may be involved in the metabolism of foreign compounds. 

It is widely known that the ATPases can be distinguished on the basis of the cations that activate them. Mg2+-, Mg2+ plus Ca2+ and Mg2+ plus Na+ and K+-ATPases are probably the best known. They are also distinguished by their localization in different subcellular organelles and by their functions, especially on account of their participation or failure to participate in a proton or Ca2+ or Na+-K+ pump. We know of no specific function assigned to the microsomal ATPases from nervous tissue. Recently Trams Lauter (1974) and Stefanovic et al. (1976) have shown that in cultured mouse neuroblastoma and glial cells the ATPases are present in the external surface of the cell. These ATPases, for which the normal relationship to their assumed substrates still has to be determined, are inactive in the presence of 1 mM EDTA and are reactivated by Ca2+, Mg2+, Mn2+, Co2+, Cd2+ and other divalent cations. 

Flavin-containing mitochondrial MAO-A and MAO-B catalyze the oxidative deamination of neurotransmitters, such as dopamine, serotonin, and norepinephrine in the central nervous system and peripheral tissues. The enzymes share 73% sequence homology and follow the same kinetic and chemical mechanism but have different substrate and inhibitor specificities. Chemical modification experiments provide evidence that a histidine residue is essential for the catalysis. There is also strong evidence that two cysteine residues are present in the active site of MAO. 

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