Co-enzyme specificity of 3-isopropylmalate dehydrogenase from Thermits thermophilus HB8 |
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Authors: | Miyazaki, Kentaro Oshima, Tairo |
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Affiliation: | Department of Life Science, Tokyo Institute of Technology Nagatsuta 4259,Yokohama 227, Japan |
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Abstract: | The coenzyme specificity of 3isopropylmalate dehydrogenasefrom an extreme thermophile, Thermus thermophilus HB8, was changedfrom NAD to NADP by sitedirected mutagenesis Based onsequence comparison of 3isopropylmalate dehydrogenasesfrom various organisms with NAD and NADPdependentisocitrate dehydrogenases, Ser226, Ser253 and De279 of 3isopropylmalatedehydrogenase were suggested as determining the coenzymespecificity. These residues were replaced with the correspondingresidues of NADPdependent isocitrate dehydrogenases;Arg, Gly and Tyr respectively. The singlemutated enzymes,S226R and I279Y, enhanced the activities towards NADP 10and 3fold respectively, whereas S253G reduced the activity.Among the multiplemutated enzymes, the doublemutatedS226R/I279Y increased the catalytic efficiency against NADP( fold) and shifted the specificity for NAD towards NADP mostsignificantly ( 173fold). |
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Keywords: | isocitrate dehydrogenase/ 3-isopropylmalate dehydrogenase/ nucleotide-binding domain/ specificity |
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