METALLOTHIONEIN-LIKE PROTEIN IN MAMMALIAN BRAIN

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Our goal is to characterize further the biochemical properties of a metallothionein-like protein recently isolated from the rat brain, and to determine its possible role in preventing neurotoxicity from heavy metals. This small molecular weight protein (Mr less than 10,000), has an elution volume (Ve/Vo) of 2.06, its synthesis is stimulated by zinc and copper but not cadmium, and the zinc-stimulated protein incorporates large quantities of [35]S-cysteine. It is hypothesized that this metallothionein-like protein may be involved (a) in zinc hemeostasis, (b) in zinc transport, (c) in metal detoxification, or perhaps (d) in events related to synaptic functions. The importance of zinc in neurochemistry and neurotoxicology becomes apparent when one realizes that zinc maintains the function and/or the structure of more than 235 metalloenzymes and/or metalloproteins known to participate in the metabolism of carbohydrates, lipids, proteins, and nucleic acids. Furthermore, chronic zinc loss is associated with cerebellar dysfunction, anorexia, hypogeusia, hyposmia, impaired night vision, anencephaly, and altered learning and behavior patterns. On the other hand, zinc excess has been detected in inherited retinal dystrophy, multiple sclerosis, Pick's disease, sudanophile leucodystrophy, and Lowe's syndrome. To what extent the brain's metallothionein-like protein is altered in these disease states is not known deserving investigation. The specific aims are to characterize further the biochemical properties of this protein by using the hepatic metallothionein as a standard and by employing techniques involving gel filtration on Sephadex G-75 columns, ion exchange chromatography on DEAE-Sephadex A-25 columns, polyacrylamide gel electrophoresis on non-denaturing gel, chromatofocusing, high performance liquid chromatography, and amino acid analysis. The possible regional distribution of metallothionein-like protein in the brain, whose zinc concentration is nonuniform, will be carried out by radioimmunoassay (RIA). In addition, the possible lipolytic activity of this protein will be assessed. Furthermore, the regulation of the synthesis of this metallothionein-like protein will be investigated by employing a culture system that uses neurons as a model and the hepatocytes as a standard: and by studying the effects of Za++, glucocorticoids and epinephrine, -ametal and hormones known to induce the synthesis of the hepatic metallothionein.