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Query: EC:1.6.99.1 (NADPH-diaphorase)
 3,903 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The organic phosphate allosteric effectors of hemoglobin, inositol hexaphosphate, 2,3-diphosphoglycerate, and ATP, interact with NADH-methemoglobin reductase (NADH-diaphorase). Significant inhibitory effects on the enzyme were found when dichlorophenolindophenol, or ferricyanide were used as electron acceptors in place of methemoglobin. In contrast, apparent stimulation of enzyme activity was observed when adult human methemoglobin was used as the electroganic phosphate on the rate of reaction due to its interaction with the substrate methemoglobin to produce the favored T type of quaternary conformation. The inhibitory effect of inositol hexaphosphate on the enzyme is associated with a perturbation in the reactivity of essential sulfhydryl group(s) on the enzyme. It is suggested that the interaction of the organic phosphate with the enzyme as well as with the substrate is significant in determining the overall rate of methemoglobin reduction.
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PMID:Inhibition of NADH-methemoglobin reductase by organic phosphates. 49 34

Erythrocytic NADH methemoglobin diaphorase acquires NADH-dichlorophenolindophenol diaphorase activity when enzyme-associated NAD is removed. This transformation is reversible and can be mediated by membrane NAD glycohydrolase (EC 3.2.2.5) in hemolysates as well as in intact cells exposed to hydrogen peroxide. It is abolished either in NADH methemoglobin diaphorase deficiency or in NAD(P) glycohydrolase (EC 3.2.2.6) deficiency which is common in Afro-American but not in European-American adults. Activities of erythrocytic NADP glycohydrolase and NAD glycohydrolase appear to depend on a single membrane enzyme.
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PMID:NAD(P) glycohydrolase deficiency in human erythrocytes and alteration of cytosol NADH-methemoglobin diaphorase by membrane NAD-glycohydrolase activity. 436 76

Human placenta contains a thermostable, cytosolic NADH-diaphorase which is different from the other diaphorases and which we designate as diaphorase P. It is specific for NADH and reduces artificial substrates such as dichlorophenol and tetrazolium derivatives, but not natural substrates such as methemoglobin, cytochrome b5 or lipoate. It is antigenically distinct from the ubiquitous red-cell type NADH-diaphorase (soluble cytochrome b5 reductase) specified by the DIA1 locus. Using electrophoretic and immunologic methods, it was possible to detect diaphorase P in various fetal tissues (brain, liver, kidney, muscle), whereas was not found in adult tissues with the exception of the brain. This enzyme, the physiological role of which remains unknown, appears to belong, therefore, to the category of fetal proteins. Its resurgance in primary liver cancer was demonstrated in three cases.
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PMID:Diaphorase P: a new fetal isozyme identified in human placenta. 624 54

The purification and properties of metlegoglobin reductase from lupine (Lupinus luteus L.) nodules are described. The purification procedure results in a 1056-fold purification of the enzyme with a total yield of 21%. The enzyme possesses the NADH-diaphorase activity. Metlegoglobin reductase is heterogenous during electrophoresis and isoelectric focusing. Electrophoresis produces two vicinal active bands, while isoelectrofocusing results in four active fractions. The fraction possessing the highest activity has a pI of 4.4. The enzyme is a flavoprotein, in which all flavins are represented by FAD. The molecular weight of the enzyme is 30 000. In some properties metlegoglobin reductase from lupine nodules is similar to methemoglobin reductase from erythrocytes and metmyoglobin reductase from muscles.
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PMID:[Properties of metlegoglobin reductase from lupine nodules]. 689 54