Properties of partially purified saccharopine dehydrogenase from human placenta. |
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Authors: | T A Fjellstedt J C Robinson |
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Affiliation: | Section on Developmental Enzymology, Laboratory of Biomedical Sciences, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20014 USA |
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Abstract: | Saccharopine dehydrogenase was previously purified 380-fold from human placenta. The enzyme was shown to catalyze the formation of α-aminoadipic-δ-semialdehyde and glutamate from saccharopine, to have a molecular weight of 480,000 on gel filtration, and not to be separable from l-lysine-α-ketoglutarate reductase. Additional properties of the saccharopine dehydrogenase are now described. The pH optimum for the conversion of saccharopine to glutamate and α-aminoadipic-δ-semialdehyde is 8.5 in Tris-HCl buffer and 8.9 in 2-amino-2-methyl-1,3-propanediol buffer. The specificity of the enzyme for Saccharopine and NAD and the inhibition by glutamate and product analogs were tested. It was found the NADP was the only cofactor that could replace NAD in the enzyme reaction and that several NAD analogs were reaction inhibitors. Glutamate was found to be only moderately effective as an inhibitor. Initial velocity studies revealed that the enzyme has an ordered reaction mechanism. The true Km values for saccharopine and NAD are 1.15 mm and 0.0645 mm, respectively. |
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