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Methylenetetrahydrofolate dehydrogenase - methenyltetrahydrofolate cyclohydrolase - formyltetrahydrofolate synthetase from porcine liver: evidence to support a common dehydrogenase-cyclohydrolase site. 1983

D Drummond, and S Smith, and R E MacKenzie

The cyclohydrolase activity of the trifunctional enzyme methylenetetrahydrofolate dehydrogenase - methenyltetrahydrofolate cyclohydrolase - formyltetrahydrofolate synthetase is inhibited by NADP+, a substrate of the dehydogenase. This uncompetitive inhibition, shown also by 3-aminopyridine adenine dinucleotide phosphate (AADP), indicates formation of dead-end complexes consisting of enzyme-nucleotide-methenyltetrahydrofolate. Chemical modification with diethylpyrocarbonate inactivates the dehydrogenase and cyclohydrolase but not the synthetase. Folate, but neither NADP+ nor AADP, protects both activities against modification. However, NADP+ potentiates the protection by folate by decreasing the apparent Kd for that ligand approximately sixfold. Chemical modification with phenylglyoxal also inactivates both the dehydrogenase and cyclohydrolase activities. Neither activity was protected by NADP+ or folate alone; however, the combination of NADP+ and folate protected both activities. These results are consistent with a model in which the dehydrogenase and cyclohydrolase activities share a common folate binding site.

UI MeSH Term Description Entries
D007700 Kinetics The rate dynamics in chemical or physical systems.
D008025 Ligases A class of enzymes that catalyze the formation of a bond between two substrate molecules, coupled with the hydrolysis of a pyrophosphate bond in ATP or a similar energy donor. (Dorland, 28th ed) EC 6. Ligase,Synthetases,Synthetase
D008099 Liver A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances. Livers
D008754 Methylenetetrahydrofolate Dehydrogenase (NADP) An NADP-dependent oxidoreductase that catalyses the conversion of 5,10-methyleneterahydrofolate to 5,10-methenyl-tetrahydrofolate. In higher eukaryotes a trifunctional enzyme exists with additional METHENYLTETRAHYDROFOLATE CYCLOHYDROLASE and FORMATE-TETRAHYDROFOLATE LIGASE activity. The enzyme plays an important role in the synthesis of 5-methyltetrahydrofolate, the methyl donor for the VITAMIN B12-dependent remethylation of HOMOCYSTEINE to METHIONINE via METHIONINE SYNTHETASE. Methylenetetrahydrofolate Dehydrogenase (NADP+),Methylenetetrahydrofolate Dehydrogenase,Dehydrogenase, Methylenetetrahydrofolate
D009097 Multienzyme Complexes Systems of enzymes which function sequentially by catalyzing consecutive reactions linked by common metabolic intermediates. They may involve simply a transfer of water molecules or hydrogen atoms and may be associated with large supramolecular structures such as MITOCHONDRIA or RIBOSOMES. Complexes, Multienzyme
D009243 NAD A coenzyme composed of ribosylnicotinamide 5'-diphosphate coupled to adenosine 5'-phosphate by pyrophosphate linkage. It is found widely in nature and is involved in numerous enzymatic reactions in which it serves as an electron carrier by being alternately oxidized (NAD+) and reduced (NADH). (Dorland, 27th ed) Coenzyme I,DPN,Diphosphopyridine Nucleotide,Nadide,Nicotinamide-Adenine Dinucleotide,Dihydronicotinamide Adenine Dinucleotide,NADH,Adenine Dinucleotide, Dihydronicotinamide,Dinucleotide, Dihydronicotinamide Adenine,Dinucleotide, Nicotinamide-Adenine,Nicotinamide Adenine Dinucleotide,Nucleotide, Diphosphopyridine
D009249 NADP Nicotinamide adenine dinucleotide phosphate. A coenzyme composed of ribosylnicotinamide 5'-phosphate (NMN) coupled by pyrophosphate linkage to the 5'-phosphate adenosine 2',5'-bisphosphate. It serves as an electron carrier in a number of reactions, being alternately oxidized (NADP+) and reduced (NADPH). (Dorland, 27th ed) Coenzyme II,Nicotinamide-Adenine Dinucleotide Phosphate,Triphosphopyridine Nucleotide,NADPH,Dinucleotide Phosphate, Nicotinamide-Adenine,Nicotinamide Adenine Dinucleotide Phosphate,Nucleotide, Triphosphopyridine,Phosphate, Nicotinamide-Adenine Dinucleotide
D010088 Oxidoreductases The class of all enzymes catalyzing oxidoreduction reactions. The substrate that is oxidized is regarded as a hydrogen donor. The systematic name is based on donor:acceptor oxidoreductase. The recommended name will be dehydrogenase, wherever this is possible; as an alternative, reductase can be used. Oxidase is only used in cases where O2 is the acceptor. (Enzyme Nomenclature, 1992, p9) Dehydrogenases,Oxidases,Oxidoreductase,Reductases,Dehydrogenase,Oxidase,Reductase
D010658 Phenylglyoxal A reagent that is highly selective for the modification of arginyl residues. It is used to selectively inhibit various enzymes and acts as an energy transfer inhibitor in photophosphorylation.
D004047 Diethyl Pyrocarbonate Preservative for wines, soft drinks, and fruit juices and a gentle esterifying agent. Diethyl Dicarbonate,Diethyl Oxydiformate,Pyrocarbonic Acid Diethyl Ester,Diethylpyrocarbonate,Ethoxyformic Anhydride,Anhydride, Ethoxyformic,Dicarbonate, Diethyl,Oxydiformate, Diethyl,Pyrocarbonate, Diethyl

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