Alpha-pyridine nucleotides as substrates for a plasmid-specified dihydrofolate reductase.
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.
D000818:Animals; D001419:Bacteria / Q000201:enzymology*; D003013:Clostridium / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology; D007536:Isomerism; D007700:Kinetics; D007780:Lacticaseibacillus casei / Q000201:enzymology; D008099:Liver / Q000201:enzymology*; D009243:NAD / Q000378:metabolism*; D009249:NADP / Q000031:analogs & derivatives* / Q000378:metabolism*; D010957:Plasmids; D051381:Rats; D013045:Species Specificity; D013379:Substrate Specificity; D013762:Tetrahydrofolate Dehydrogenase / Q000235:genetics* / Q000378:metabolism
D009243:NAD; D009249:NADP; D013762:Tetrahydrofolate Dehydrogenase