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.
Nardini
M
M
Department of Biochemical Sciences, University of Rome, La Sapeinza, Italy.
Ricci
G
G
Caccuri
A M
AM
Solinas
S P
SP
Vesci
L
L
Cavallini
D
D
D000603:Amino Acids, Sulfur / Q000378:metabolism; D000818:Animals; D002384:Catalysis; D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D007525:Isoelectric Focusing; D007672:Kidney Cortex / Q000201:enzymology; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D010084:Oxidation-Reduction; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000302:isolation & purification*; D013379:Substrate Specificity; D013552:Swine; D013841:Thiazepines / Q000378:metabolism*
D000603:Amino Acids, Sulfur; D013841:Thiazepines; D007770:L-Lactate Dehydrogenase; D000587:Oxidoreductases Acting on CH-NH Group Donors; C056073:ketimine reductase