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Clvi . Studies on Amino-acid Dehydrogenase
| Content Provider | Semantic Scholar |
|---|---|
| Copyright Year | 2005 |
| Abstract | IT has been shown by many workers, especially by Knoop [1925] and Krebs [1933], that amino-acids are oxidised by tissues in vitro. It has later been reported by Bemheim and Bernheim [1934; 1935] and Krebs [1935] that a cellfree extract of tissues can also oxidise aerobically many amino-acids, and the former authors claim to have obtained an enzyme from tissue extracts which can decolorise methylene blue more rapidly in presence of proline, phenylalanine, valine, leucine, serine etc. The present work is a study of the mechanism of oxidative deamination of amino-acids by cell-free dehydrogenases. It has been shown that dehydrogenases such as alcohol dehydrogenase, glucose dehydrogenase, hexosemonophosphate dehydrogenase etc. require the presence of a low-molecular co-enzyme; that is to say the active enzyme (holo-dehydrogenase) consists of a high-molecular group (apo-dehydrogenase) and a low-molecular prosthetic group (co-dehydrogenase), the components of the holo-dehydrogenase being in dissociation equilibrium. Up to the present time two co-enzymes (co-dehydrogenases) are known, namely co-zymase (co-dehydrogenase I) and the co-ferment of Warburg and Christian [1935] (co-dehydrogenase 11).2 These co-enzymes act by taking up activated hydrogen from the substrate, thereby forming the reduced co-enzymes which are not autoxidisable but are reoxidised by flavin-enzyme. The leucoflavin-enzyme itself can act directly with molecular oxygen or with a reducible dye like methylene blue. It seemed to be of interest to investigate whether amino-acid dehydrogenase has anything to do with co-enzyme-flavin-enzyme catalysis. The fact that amino-acid oxidation by cell-free extracts was not inhibited by KCN made it possible that it might be such a metal-free system in which co-enzymeflavin-enzyme catalyses the reaction. In the present work the problem has been studied with reference to proline. None of the known activators like co-zymase (Euler), co-dehydrogenase II [Warburg and Christian, 1935; Euler and Adler, 1935, 3; 1936], flavin-enzyme [Warburg and Christian, 1932, 1, 2], glutathione, ascorbic acid, adenylpyrophosphate can activate proline dehydrogenase except glutathione in higher concentrations. (This may be due to some inhibiting metal which cannot be bound by lower concentrations of glutathione.) The facts that the dehydrogenase is not catalysed by flavin-enzyme and that anaerobic reduction of dyes is relatively much slower than the oxidation by molecular oxygen seem to indicate that flavin-enzyme is not a necessary component of the system. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.biochemj.org/content/ppbiochemj/30/6/1080.full.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
