| Literature DB >> 6410395 |
Abstract
The alpha epimers of pyridine nucleotides are almost totally inactive as reductants in dehydrogenase reactions. In contrast, the R plasmid R67-specified dihydrofolate reductase (5,6,7,8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) isolated from trimethoprim-resistant Escherichia coli utilized alpha-NADPH and alpha-NADH in addition to the "normal" beta-epimers. The enzymes from bacterial and mammalian sources used only beta-NADPH and beta-NADH. THe Km value for alpha-NADPH (16 microM) was 4-fold greater than that for beta-NADPH (4 microM), while the maximal velocity of the alpha-NADPH-catalyzed reaction was 70% of that seen with the beta-NADPH. beta-NADP+ and alpha-NADP+ were competitive inhibitors of the R67 enzyme. Pyridine nucleotide analogues such as deamino- and acetyl-NADPH were used readily by bacterial, plasmid, and mammalian enzymes, whereas thio-NADPH was used only by the plasmid enzyme. These data suggest that the enzyme from R plasmid R67 possesses a pyridine nucleotide binding site different from that of other dihydrofolate reductases and dehydrogenases.Entities:
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Year: 1983 PMID： 6410395 PMCID： PMC384095 DOI： 10.1073/pnas.80.15.4619
Source DB: PubMed Journal: Proc Natl Acad Sci U S A ISSN： 0027-8424 Impact factor: 11.205