Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:Q8NEX9 (reductase)
 26,410 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Measurements of the activity of transketolase in human erythrocyte lysates by an assay coupled to NADH oxidation indicate that interactions of assay substrates with hemoglobin can give rise to overestimations of transketolase activity. Three potential sources of error are identified. Thus, in lysates containing methemoglobin, NADH oxidation can be due firstly to methemoglobin reductase activity or secondly to the monooxygenase activity of methemoglobin, for which the substrate can be ribose 5-phosphate, a substrate also of transketolase. Thirdly, the addition of high concentrations of the transketolase cofactor, TDP, to an insufficiently buffered reaction mixture can cause the aggregation and precipitation of hemoglobin: a phenomenon that may be misconstrued as an enhanced increase in absorbance at 340 nm and hence as additional transketolase activity. Although the present study concentrates on these potential artefacts in assays of transketolase activity, the findings may well be relevant to the measurement of other enzyme activities in hemolysates by procedures based ultimately on the rate of consumption or production of NAD(P)H.
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PMID:Interactions with hemoglobin: a source of error in measurements of transketolase activity in hemolysates. 274 79

Pure methemoglobin was prepared from fresh red cells and was used as substrate for methemoglobin reduction reaction. Two sources of methemoglobin reductase were used: (a) red cell hemolysate which was prepared by freezing and thawing of unwashed red cells; (b) purified methemoglobin reductase from bank blood. Methemoglobin reduction rate was measured in a mixture of pure methemoglobin (substrate) and hemolysate (enzyme). In other experiments the rate of methemoglobin reduction was measured in the above mixture with the addition of various other compounds such as NADH, cytochrome b5, and pure methemoglobin reductase. Only the addition of pure enzyme accelerated the rate of methemoglobin reduction. In other experiments, the rate of methemoglobin reduction was measured when the reduction reaction was carried out in the presence of various amounts of deoxyhemoglobin, globin, or albumin. It was shown that all proteins tested here decreased the reduction rate. It is concluded that (a) in the red cell, under normal conditions, only the activity of the methemoglobin reductase controls the speed of methemoglobin reduction, and (b) the inhibition of methemoglobin reduction by reduced hemoglobin is mostly nonspecific suggesting a noncompetitive reaction.
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PMID:Methemoglobin reduction under near physiological conditions. 277 61

Two cases of the congenital methemoglobinemia in children due to the deficiency of NADH-dependent methemoglobin reductase in erythrocytes. These children were referred to the Cardiological Ward at the Child Health Centre with suspected cyanotic heart defect. Cardiological examinations excluded heart defect but an increased blood methemoglobin level and decreased activity of NADH-dependent methemoglobin reductase were found, that caused methemoglobinemia. Methylene blue and vitamin C diminished cyanosis. These cases advocate inclusion of methemoglobinemia into differential diagnosis of cyanotic disorders especially if there is no evident pathology in cardio-vascular system.
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PMID:[Cyanosis in children caused by inherited methemoglobinemia due to deficiency of NADH-dependent methemoglobin reductase in erythrocytes]. 281 7

A 7-week-old infant with methemoglobinemia, hemolytic anemia, and inadequate weight gain was found to have a Campylobacter jejuni gastrointestinal tract infection. Known etiologies of methemoglobinemia such as oxidative drug exposure, deficiency of NADH-methemoglobin reductase, and hemoglobin M disorder were excluded. The patient had a twin brother (probably identical) who had neither methemoglobinemia nor stool cultures positive for C. jejuni. The twin essentially served as an experimental control, making other environmental or genetic causes of methemoglobinemia unlikely in the patient. Both the methemoglobinemia and the C. jejuni infection responded to adequate treatment with erythromycin. The association of a C. jejuni infection with methemoglobinemia is discussed in light of previous associations of enteritis and methemoglobinemia in infants.
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PMID:Methemoglobinemia and hemolytic anemia associated with Campylobacter jejuni enteritis. 318 15

A spectrophotometric method has been developed that uses extracellular hemoglobin (Hb) to trap nitric oxide (NO) released during denitrification as nitrosyl hemoglobin (HbNO). The rate of complexation of NO with Hb is about at the diffusion controlled limit for protein molecules and the product, HbNO, is essentially stable. Hb was added to an anaerobic bacterial suspension and denitrification was initiated with either KNO2 or KNO3. HbNO formation was observed for six species of denitrifying bacteria and showed isosbestic points at 544, 568, and 586 nm. Cellular NO production, presumably by nitrite reductase, was kinetically distinct from the much slower chemical reaction of Hb with KNO2 to form methemoglobin and HbNO. The rate of HbNO formation was proportional to cell density, essentially independent of pH from 6.8 to 7.4, nearly zero order in [Hb] and, at least with Paracoccus denitrificans, strongly inhibited by rotenone and antimycin A. The Cu chelator, diethyldithiocarbamate, had no effect on HbNO formation by Pa. denitrificans, but abolished that by Achromobacter cycloclastes which uses a Cu-containing nitrite reductase known to be inactivated by the chelator. HbNO formation did not occur with non-denitrifying bacteria. The stoichiometry at high [Hb] for conversion of Hb to HbNO was 1.3-1.8 KNO2 per Hb for Pa. denitrificans, Pseudomonas aeruginosa, and A. cycloclastes and about 3.4 for Pseudomonas stutzeri. The former range of values corresponds to a partition of about 2 N atoms in 3 toward trapping and 1 in 3 toward reduction on the pathway to N2. Nitrogen not trapped appeared largely as N2O in presence of acetylene. The results are consistent with a model in which NO is a freely diffusible intermediate between nitrite and N2O, providing that nitric oxide reductase is or nearly is a diffusion controlled enzyme.
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PMID:Trapping of nitric oxide produced during denitrification by extracellular hemoglobin. 333 13

The case of a 3-week-old male infant is described. After receiving an iatrogenic overdose of metoclopramide (1.0 mg/kg every six hours) throughout a 36-hour period for the treatment of suspected gastroesophageal reflux, he became cyanotic, lethargic, and irritable, he fed poorly, and he had diarrhea and respiratory distress. Methemoglobinemia (20.5%) and reduced oxyhemoglobin saturation (79%) were identified. The patient had an excellent clinical response following a single IV dose of methylene blue. Subsequently, methemoglobin reductase activity was normal and there was no measurable hemoglobin M. The diagnosis of methemoglobinemia should be considered in any infant receiving large doses of metoclopramide who has clinical findings of cyanosis, ashen color, or a history of lethargy and/or motor restlessness.
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PMID:Metoclopramide-induced methemoglobinemia. 340 65

Addition of hemoglobin, methemoglobin, hemin or hematin in the assay mixture of rat liver 3-hydroxy-3-methylglutaryl CoA (HMGCoA) reductase inhibited the activity of the enzyme. The inhibition by hemin was rapid, without any apparent dependence on time of preincubation. At 20 microM hemin, a maximum of about 50% inhibition was obtained in the case of the microsomal enzyme while the solubilized enzyme showed almost 80% inhibition. Dithiothreitol at high concentrations or either of the two substrates of the enzyme (HMGCoA and NADPH) could afford partial protection when added before hemin. The Km for both the substrates increased in the presence of hemin. The inhibition by hemin appeared to be irreversible, the presence of KCN or NaN3 being the only means of preventing the inhibition. Molecular oxygen was required for the inhibition. Oxygen radicals and H2O2, however, did not seem to be involved. This offered a clue that an oxidation reaction of the reductase protein may be the likely mechanism of its inactivation. The enzyme protein did not, however, get degraded under the conditions of inhibition.
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PMID:Hemin-mediated oxidative inactivation of 3-hydroxy-3-methylglutaryl CoA reductase. 343 83

In stroma-free hemoglobin solution (SFHS) formation of methemoglobin (hemiglobin; Hi) occurs over a period of some months, due to the fact that Hi reduction stops in hemolysates. SFHS should contain active hemoglobin (Hb), which is able to bind oxygen and should not contain inactive Hb (Hi, carboxyhemoglobin) which does not bind oxygen. Reversible binding of oxygen by Hb is only possible when the molecule is in its reduced (Fe++) form. In red blood cells (RBC) Hb is in the reduced form. The formation of Hi, which contains Fe as a result of Hb oxidation, is the first step in Hb degradation. This step is reversible in RBC. Previously, we have described the preparation of SFHS containing the methemoglobin reductase (MR) system of RBC. To improve the stability of SFHS, we first investigated the formation of Hi as a function of pH and ionic strength and quantified the MR activity in SFHS. Non-enzymatic Hi reduction was studied with substances as ascorbate and glutathione. Stimulation of MR by EDTA was tested. Inhibition of Hi formation was studied with nicotinic acid amide in the presence and absence of NADH. It is concluded that ascorbate and glutathione are not effective during extended periods of storage of SFHS, and that EDTA causes formation of large amounts of Hi. Nicotinic acid amide did not inhibit Hi formation. NADH, as a substrate for the MR system, is very effective in keeping Hi low.
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PMID:Quality control material containing hemoglobin for blood gas and pH measurement: improvement of the stability of stroma-free hemoglobin solution. 348 83

HMP pathway activity changes occurring after exposure to ionizing radiation (LD50 dose) have been investigated. The study was carried out on 18 experimental guinea pigs subjected to 5 successive exposures of 150 rads 3 or 4 days apart. The control animals were sham radiated but were otherwise treated identically as those of the experimental groups. Blood samples were taken by cardiac puncture before radiation and 30 min after each exposure of 150 rads. The red cells were re-suspended in their own plasma and HMP pathway activity was measured in the suspension. The pathway activity showed a consistent but minor reduction in the experimental group, which became statistically significant after the total dose of 750 rads (P less than 0.020). In a separate study the changes induced by ionizing radiation in the erythrocyte enzyme NADH-methemoglobin reductase were measured using the same experimental protocol. The enzyme activity in the red cells of the experimental group varied between 34.90 +/- 2.17 to 161.95 +/- 5.34 I.U./ml erythrocyte pack. Its activity declined toward the initial value after reaching the peak by the 12th day of ionizing radiation with 600 rads (P less than 0.001).
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PMID:Changes of hexose monophosphate pathway and methemoglobin reductase enzyme activity after radiation in guinea pigs. 358 90

Rate of methemoglobin reduction was increased in erythrocyte hemolysates in presence of 4-N-(p-sulfanilino)-5-methoxy-1.2-benzoquinone. Kinetic parameters of total reaction and of individual steps showed that the substance and other amino-derivatives of ortho-benzoquinone could be used for estimation of methemoglobin reductase activity.
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PMID:[A method of determining NADH-methemoglobin reductase activity using amino derivatives of o-benzoquinone]. 363 8


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