Purification and characterization of a ketimine-reducing enzyme.
An NAD(P)H-dependent reductase able to reduce a new class of cyclic unsaturated compounds named ketimines has been detected and purified 2500-fold from pig kidney. Some molecular and kinetic properties of this enzyme have been determined. The enzymatic reduction proceeds with a classical ping-pong mechanism and some results suggest that the true substrate has the ketiminic structure and is in equilibrium with the enaminic and keto-open forms. As previously described, ketimines arise from the deamination of a number of sulfur-containing amino acids, i.e. L-cystathionine, L-lanthionine and S-aminoethyl-L-cysteine, catalyzed by a widespread mammalian transaminase. The enzymatic reduction products of ketimines have been identified as cyclothionine, 1,4-thiomorpholine 3,5-dicarboxylic acid and 1,4-thiomorpholine 3-carboxylic acid. Some of these compounds have been detected in mammals, thus suggesting a possible role of this enzyme in their biosynthesis.[1]References
- Purification and characterization of a ketimine-reducing enzyme. Nardini, M., Ricci, G., Caccuri, A.M., Solinas, S.P., Vesci, L., Cavallini, D. Eur. J. Biochem. (1988) [Pubmed]
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