Relationship between the rate of erythrocyte hexose monophosphate pathway and the glucose 6-phosphate concentration

Erythrocytes of individuals with increased (+ 50%) or reduced (-35%) hexokinase activity contain respectively 70 and 17 nmole/ml RBC of glucose-6-phosphate (normal concentration 30 +/- 5nmole/ml RBC) and show comparable rates of the HMP (60 +/- 5nmole/hr/ml RBC). Similarly, in RBC of different ages, obtained by density gradient ultracentrifugation, the glucose-6-phosphate concentration range from 57 (young cells) to 18 (old cells) nmole/ml RBC but the rate at which glucose is utilized in the HMP is unchanged. These data exclude a regulatory role of glucose 6-phosphate in the HMP even if its concentration is under that required for maximal G6PD activity.

Proton stoichiometry associated with human neutrophil respiratory-burst reactions

Control of the intraphagosomal pH in neutrophils may be of importance in creating a microbicidal environment by regulating the activity of the O2-.-generating NADPH oxidase and the lysosomal enzymes discharged into this compartment. In this study, we examined the proton stoichiometry associated with the primary enzymatic reaction underlying the respiratory burst. A preparation of the neutrophil-derived, membrane oxidase consumed NADPH and generated O2-. with a stoichiometry of 1 NADPH:2 O2-. When the enzymatically produced O2-. was prevented from undergoing dismutation, net protons were released in an approximate 1:2 stoichiometry with O2-. generated. In contrast, when O2-. was allowed to dismutate to H2O2, net protons were consumed in a 1:1 stoichiometry with the accumulated H2O2. Thus, the delta pH associated with the NADPH oxidase-dependent production of O2-. was dictated by the fate of the generated radical. The consumption of the oxidase-generated H2O2 by the lysosomal enzyme myeloperoxidase resulted in the formation of HOCl which was trapped in the presence of taurine as the N-chloro derivative. The ratio of chlorinated product formed to H+ consumed was 1:1. The implications of these results are discussed in terms of the known intraphagosomal pH changes that occur following neutrophil stimulation. We conclude that the O2-.-generating oxidase plays a dual role in the phagosome by simultaneously creating an oxidizing environment that optimizes pH-dependent microbicidal processes.

[Metabolism of fatty acids in the healthy myocardium and in ischemia]

Data on absorption and consumption in heart tissue of free and ester-bound fatty acids from blood lipids are discussed. Preferential utilization of individual fatty acids in heart tissue from blood lipids is considered. Dependence of fatty acid metabolism on the activity of tricarboxylic acid cycle, interrelationship between metabolism of endogenous and exogenous fatty acids in heart muscle are considered. The data are analyzed on pathways of exogenous fatty acids turnover in tissues, their conversion into endogenous fatty acids, specific for individual tissue, cells and their organelles. Development of syndrome of unsaturated fatty acids deficiency, induced by incomplete fatty diet, is discussed. Metabolism of fatty acids in heart under conditions of oxygen deficiency is considered. The data are reviewed on the effects of hypoxia on metabolism of fatty acids in myocardium. Carbohydrate and fatty acid consumption in heart muscle, typical alterations in fatty acid incorporation into heart lipids, effect of fatty acids excess on functioning of sarcoplasmic reticulum and mitochondrial membranes are discussed.

The effect of glyceraldehyde on red cells. Haemoglobin status, oxidative metabolism and glycolysis

Glyceraldehyde induces changes in the flux of glucose oxidised through the hexose monophosphate pathway, the concentrations of intermediates in the Embden-Meyerhoff pathway, the oxidative status of haemoglobin and levels of reduced and oxidised pyridine nucleotides and glutathione in red cells. Glyceraldehyde autoxidises in the cellular incubations, consuming oxygen and producing glyoxalase I- and II-reactive materials. Major fates of glyceraldehyde in red cells appear to be: (i) adduct formation with reduced glutathione and cellular protein; (ii) autoxidation and reaction with oxyhaemoglobin and pyridine nucleotides, and (iii) phosphorylation of D-glyceraldehyde and entry into the glycolytic pathway as glyceraldehyde 3-phosphate. The production of glycerol from glyceraldehyde by red cell L-hexonate dehydrogenase appears not to be a major reaction of glyceraldehyde in red cells. These results indicate that high concentrations of glyceraldehyde (1-50 mM) may induce oxidative stress in red cells by virtue of the spontaneous autoxidation of glyceraldehyde, forming hydrogen peroxide and alpha-ketoaldehydes (glyoxalase substrates). The implications of glyceraldehyde-induced oxidative stress for the in vitro anti-sickling effect of DL-glyceraldehyde and for the polyol pathway metabolism of glyceraldehyde are discussed.

Reactions of nitrosochloramphenicol in blood

It has been suggested that nitrosochloramphenicol (NOCAP), a possible metabolite of chloramphenicol (CAP), may be involved in CAP-induced aplastic anemia. We found that NOCAP was rapidly eliminated from human blood in vitro (more than 90% in less than 15 sec). Analysis of the different reactions showed that 5% of NOCAP was covalently bound to plasma proteins, mainly to albumin, the remainder being metabolized in red cells. The most important reaction in red cells was the very rapid adduct formation with GSH (k = 5,500 M-1S-1), yielding presumably a semimercaptal which either isomerized to a sulfinamide (GSONHCAP, k = 0.05 s-1) or was thiolytically cleaved by another GSH molecule with formation of the hydroxylamine (NHOHCAP) and GSSG (k = 7.1 M-1S-1). Another important elimination reaction was the covalent binding of NOCAP to the SH groups of hemoglobin (k = 5M-1S-1), also yielding a sulfinamide. Besides these reactions with thiols, NOCAP was enzymatically reduced to NHOHCAP in the presence of NADPH (Km NADPH = 10(-5) M; Km NOCAP = 10(-4) M; Vmax = 2 mumole/min per ml). This reaction was only effective at NOCAP concentrations below 10(-4)M, probably because of limited NADPH-regeneration. Further reduction of NHOHCAP to NH2CAP was a slow process which did not exceed 0.5 nmole/min per ml. NH2CAP was mainly formed from GSONHCAP, a reaction which depended on NADPH and the presence of hemolysate, indicating an enzymatic reaction. In contrast to smaller nitrosoarenes, NOCAP was a poor ligand for ferrohemoglobin (probably due to steric hindrance by its bulky molecule) and was therefore much more exposed to biotransformation. NOCAP and NHOHCAP formed ferrihemoglobin at a rate 5000 times slower than did phenylhydroxylamine. In contrast to NOCAP, NHOHCAP penetrated slowly the red cell membrane (4 about 5 min), and its disposition in blood was quite ineffective. From these data, it seems likely that most of the NOCAP formed by microorganisms in the intestine or produced in the liver, will be degraded in blood before it can reach the bone marrow.

The effect of pyrroline-5-carboxylic acid on nucleotide metabolism in erythrocytes from normal and glucose-6-phosphate dehydrogenase-deficient subjects

Pyrroline-5-carboxylate, the intermediate in the interconversion of proline, ornithine, and glutamate, increases 5-phosphoribosyl 1-pyrophosphate (PP-ribose-P) and purine nucleotide formation in intact human erythrocytes. We proposed that: 1) pyrroline-5-carboxylate is converted to proline by pyrroline-5-carboxylate reductase with concomitant oxidation of NADPH, 2) NADP+ augments glucose-6-phosphate dehydrogenase activity, and 3) production of ribose-5-phosphate via the pentose shunt is increased. Since glucose-6-phosphate dehydrogenase plays a central role in this proposed mechanism, we examined the responsiveness of glucose-6-phosphate dehydrogenase-deficient erythrocytes to pyrroline-5-carboxylate. We compared erythrocytes from four Sardinian glucose-6-phosphate dehydrogenase-deficient subjects and four Sardinian normal controls. Without pyrroline-5-carboxylate treatment, the levels of pentose shunt activity, PP-ribose-P, and inosine monophosphate were comparable in the two populations. However, the response to pyrroline-5-carboxylate in erythrocytes from normal and glucose-6-phosphate dehydrogenase-deficient subjects was markedly different. In normal erythrocytes, pyrroline-5-carboxylate treatment increased pentose shunt activity 600%, PP-ribose-P formation 250%, and the incorporation of hypoxanthine into inosine monophosphate 260%. In contrast, pyrroline-5-carboxylate had no effect on glucose-6-phosphate dehydrogenase-deficient erythrocytes. These findings strongly support our proposed mechanism for the pyrroline-5-carboxylate effect on nucleotides. Furthermore, the markedly different capacities for nucleotide synthesis in the two populations with pyrroline-5-carboxylate treatment suggest a role for pyrroline-5-carboxylate-mediated modulation of nucleotide metabolism in normal cells.

Fast reversed-phase high-performance liquid chromatographic determination of nucleotides in red blood cells

A method for the accurate determination of ATP, ADP, AMP, NADP and NAD in 20 min in red blood cell extracts by reversed-phase high-performance liquid chromatography is described. Experimental parameters affecting the separation are discussed.

Short communication. Glycogenosis Ib: neutrophil microbicidal defects due to impaired hexose monophosphate shunt

We studied neutrophil microbicidal function and oxidative metabolic activity in a patient with glycogenosis Ib. The intracellular killing defect and the respiratory burst abnormality in gycogenosis Ib neutrophils were confirmed. The impaired oxygen-dependent microbicidal activity was shown to result from impaired hexose monophosphate shunt activity (impaired endogenous NADPH synthesis) and could be corrected by homogenization of the cells, followed by the addition of exogenous NADPH. Our data are thus consistent with a possible role for glucose-6-phosphate transport in neutrophil microbicidal function. We recommend a continuous prophylaxis with co-trimoxazole in patients with glycogen storage disease Ib.

[Nicotinic acid metabolism in patients with non-coronarogenic heart diseases]

To study the supply with nicotinic acid, 74 patients with rheumatic fever of varying degree and circulatory disorders, 10 patients with infectious-allergic myocarditis, 15 with tonsilogenous myocardiodystrophy were examined. Seventy normal subjects served as control. The supply with vitamin PP was evaluated from the blood content of NAD, NADP and N'-methylnicotinamide and its excretion with urine. All the patients with myocarditis and rheumatic fever demonstrated a decrease in the nicotinic acid supply which became more marked as the degree of rheumatic fever rose and circulatory failure supervened. In patients with tonsilogenous myocardiodystrophy , the disturbance of the vitamin supply was less overt.

Examination of the oxidase function of the b-type cytochrome in human polymorphonuclear leucocytes

The spectral properties of a particulate fraction of human polymorphonuclear neutrophils capable of oxidizing NADPH were studied before and after depletion of myeloperoxidase by KCl treatment. Difference spectra (dithionite reduced minus oxidized) at 77 K of non-extracted particles showed peaks of a b-type cytochrome at 556, 527 and 425 nm and of myeloperoxidase at 636 and 474 nm. Extraction of myeloperoxidase led to a 4-5-fold increase in the size of the cytochrome b peaks. In non-extracted particles, the CO-reduced spectra at 77 K revealed a typical CO-reduced myeloperoxidase complex with new peaks at 625-630 and 462 nm, and a limited shift of the Soret band of reduced cytochrome b from 425 to 424-423 nm. The same shift was observed for cytochrome b in extracted particles. Photoirradiation of the CO-dithionite-reduced particles resulted in a back shift of the CO-reduced peaks to their original positions in the reduced spectrum. Concomitantly, the size of the peaks both for myeloperoxidase and cytochrome b was increased, indicating photoreduction. Cytochrome b and myeloperoxidase in neutrophil particles were poorly reduced by NADPH; reduction occurred upon photoirradiation. FAD and FMN added to particles in the presence of NADPH were photoreduced concomitantly with cytochrome b. Addition of phorbol myristate acetate to intact neutrophils in the presence of glucose resulted in CO- and cyanide-insensitive respiration, accumulation of O-2, and also in reduction of cytochrome b. The lag required to reach the steady-state production of O-2 was equal to the lag required for cytochrome b to reach a plateau of reduction. The data are consistent with the idea that cytochrome b in neutrophils might belong to a branched pathway that is not rate-limiting in the cyanide-resistant respiration of the neutrophils.

A mechanism for primaquine mediated oxidation of NADPH in red blood cells

The incubation of NADPH with primaquine results in the formation of free radicals which were demonstrated by the electron spin resonance (ESR) technique of spin trapping using 5,5-dimethyl-l-pyrroline-N-oxide (DMPO) as the spin trap. The free radicals formed were identified as the superoxide (DMPO-OOH) and hydroxyl (DMPO-OH) spin adducts of DMPO. Copper/zinc superoxide dismutase inhibited the formation of DMPO-OOH while it only partly inhibited the formation of DMPO-OH which could be totally inhibited by catalase. This indicates that the formation of hydroxyl radicals is not totally arising from the Haber-Weiss reaction. However since the formation of hydroxyl radicals is dependent on hydrogen peroxide, a non-metal catalysed reduction of hydrogen peroxide is postulated for their formation. Oxygen consumption during the reaction between primaquine and NADPH was found to be consistent with the spin trapping experiments and the rate of production of DMPO-OH indicates the formation of 1:1 catalytic complex between the two reactants. Quenching of the fluorescence of NADPH at 460 nm in the presence of primaquine indicates the formation of a charge transfer complex. When red blood cells are incubated with primaquine a hydroxyl spin adduct (DMPO-OH) is observed. The formation of this radical is probably the main cause of primaquine mediated toxicity.

[Use of nicotinamide for correcting the disordered nicotinic acid allowance of patients with noncoronarogenic heart diseases]

A study was made of the effects of different doses of nicotinamide (NA) on the nicotinic acid supply in 37 patients with rheumocarditis of varying severity without circulation failure, in 5 patients with infectious-allergic myocarditis, and in 10 patients with tonzilogenous myocardiodystrophy. Twenty-eight patients with analogous diseases given unified therapy without NA and 70 healthy subjects were examined for control purposes. The rate of vitamin PP supply was evaluated from the content of NAD and NADP in red cells, from that of N'-methylnicotinamide in the blood and its excretion with urine. Administration of NA in a dose of 50 mg a day for 2 weeks to patients with tonsilogenous myocardiodystrophy made the indicators under consideration return to normal. The attainment of complete correction of abnormal vitamin PP supply in patients with rheumocarditis and infectious-allergic myocarditis demands a 2-time increase of the drug dose.

G6PD Varadero. A new variant of glucose-6-phosphate dehydrogenase associated with congenital nonspherocytic hemolytic anemia

A glucose-6-phosphate dehydrogenase (G6PD) variant was studied in a mulatto patient with chronic nonspherocytic hemolytic anemia. This variant has reduced activity, increased thermolability, a reduced Michaelis constant for glucose-6-phosphate, slightly increased electrophoretic mobility, a biphasic pH activity profile, high 2-deoxyglucose-6-phosphate utilization, normal diamino nicotinamide adenine dinucleotide phosphate utilization and a peak of elution profile after G6PD B. The electrophoretic, kinetic, and chromatographic properties of this erythrocyte G6PD variant allow the conclusion that G6PD Varadero is probably a new variant.

Factors influencing the metabolic pathways of glucose in human erythrocytes

The metabolic effect of a lactate or pyruvate load and methylene blue (Mb) on hexose monophosphate shunt (HMPS) and Embden-Meyerhof pathway (EMP) were investigated in intact erythrocytes in the presence of glucose. Pyruvate enhances glucose consumption and 14CO2 production, lactate reduces 14CO2 production but glucose consumption is unchanged. These effects are dependent on the lactate and pyruvate concentrations in the buffer. A pyruvate load does not results to influence the net production of pyruvate, which is conversely markedly increased by Mb. The lactate load raises slightly the total pyruvate level but its rate of production is unchanged, with respect to that of the control. A considerable effect on the intracellular to extracellular pyruvate ratio is observed in these different conditions, as well as modifications in the levels of inorganic phosphate (Pi).

Glutathione reductase from human erythrocytes. The sequences of the NADPH domain and of the interface domain

1. Sequence analysis of the NADPH domain (residues 158--293) and of the interface domain (365--478) was based on 12 CNBr fragments, which were isolated using ion-exchange chromatography and paper methods. Fragments with more than 15 residues were digested further with trypsin and chymotrypsin. The isolated peptides were sequenced by automated solid-phase Edman degradation. All sequenced peptides were ordered and overlapped by computerized comparisons with a complete sequence guessed from the electron density map of the protein. In the case of short CNBr fragments, this alignment was confirmed by the sequence analysis of protein fragments resulting from incomplete CNBr cleavage. 2. In the NADPH domain, residue 197, which is involved in an induced-fit mechanism, was identified as a tyrosine. The structure of the NADPH domain is probably homologous with the NAD domain of lipoamide dehydrogenase and with the FAD domain of several proteins, but not with NADPH domains of known chain-fold in other proteins. 3. The paper completes the sequence analysis of glutathione reductase so that the enzyme is now known in atomic detail. The numbering scheme of the chemically determined sequence will be used henceforth in crystallographic studies also. As inferred from the sequence data each of the two identical chains contains 478 amino acid residues, the composition being Cys10, Asp21, Asn17, Thr31, Ser31, Glu29, Gln11, Pro24, Gly43, Ala42, Val44, Met15, Ile29, Leu34, Tyr13, Phe14, Lys34, His16. Arg17, and Trp3. From these data an Mr of 2 x 51 600 was calculated for the FAD-free apoenzyme and an Mr of 2 x 42 400 for the holoenzyme.

[Interaction of the Embden-Meyerhof pathway and hexose monophosphate shunt in erythrocytes]

A mathematical model of glycolysis in human erythrocytes for the interaction between the Embden-Meyerhof and the pentose phosphate pathways has been developed. The characteristic surfaces, i. e. interdependencies between the rates of metabolite flows in both pathways and ATP and NADPH concentrations have been calculated. The model obtained is well correlated with the experimental data on glycolysis characteristic at low rates of the pentose phosphate pathway reactions. The model suggests that NADPH and GSH concentrations should be stabilized. At ATP and NADPH concentrations close to the physiological ones the Embden-Meyerhof and pentose phosphate pathways function practically independently. When the NADPH concentration is decreased below 80% of the physiological value, the system ceases to stabilize the ATP concentration. In its turn, a decrease of ATP concentration results in a corresponding decrease of the maximal rate of the pentose phosphate pathway.

Pyrroline-5-carboxylate reductase in human erythrocytes

Pyrroline-5-carboxylate reductase, which converts pyrroline-5-carboxylate to proline, has been identified in human erythrocytes. The level of pyrroline-5-carboxylate reductase activity in these cells is comparable to the activity levels of major erythrocyte enzymes. The physiologic function of the enzyme in erythrocytes cannot be related to its function in other tissues, i.e., producing proline for protein synthesis. We examined the kinetic properties of erythrocyte pyrroline-5-carboxylate reductase and compared them to the properties of the enzyme from proliferating cultured human fibroblasts. We found that the kinetic properties and regulation of the erythrocyte enzyme are distinctly different from those for human fibroblast pyrroline-5-carboxylate reductase. These characteristics are consistent with the interpretation that the function of the enzyme in human erythrocytes may be to generate oxidizing potential in the form of NADP+.

Genetic variation in erythrocyte NAD levels in the mouse and its effect on glyceraldehyde phosphate dehydrogenase activity and stability

During a screening of inbred strains for enzyme variation in glycolysis, differences were found in glyceraldehyde phosphate dehydrogenase (GAPDH) activity between C57BL/6J and SM/J mice. Segregation analysis did not reveal unequivocal monogenic inheritance. Dialysis of hemolysates caused decay of enzyme activity, especially in C57BL animals, which could be prevented by the presence of NAD. This led to the finding that erythrocyte NAD levels were threefold higher in SM than C57BL animals and, although additively inherited, did not appear to be monogenic. This is comparable with but independent of the differences and effect of erythrocyte NADP levels on glucose-6 phosphate dehydrogenase activity reported by R. P. Erickson (1974) Biochem. Genet. 11:33] and emphasizes the range of mechanisms that can be involved in the genetic control of enzyme activity in mammalian systems.

[Content of nicotinamide coenzymes, metabolites and the NAD-dependent dehydrogenase activity in the blood in arteriosclerosis]

Study of the key mechanisms, metabolism regulators, showed that in the blood of patients with atherosclerosis the NAD/NAD . N ratio decreases by 59.8% and the NAD+ concentration by 44%, while the NAD . N content increases by 56.7%. In the nicotinamide adenine dinucleotide system there is a general tendency tomards accumulation:the concentration of NADP+ grows by 218.6% and that of NADP . N by 12.9%. A marked increase in the content of incompletely oxidized products is determined: lactic acid by 37.4%, alpha-glycerophosphate by 49.8%, dihydroxyacetone phosphate by 155%, oxaloacetate by 131% in the presence of lactate dehydrogenase and malate dehydrogenase activation. The detected changes are evidence of tissue energy debt in atherosclerosis, they reflect the character of metabolic acidosis formation and point to the presence of conditions for intensified liposynthesis.

Favism: erythrocyte metabolism during haemolysis and reticulocytosis

The reduced activity of glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate; NADP+ 1-oxidoreductase; G6PF) in Mediterranean erythrocytes explains the precarious equilibrium of the hexose monophosphate pathway (HMP) and the susceptibility of these cells to haemolytic agents. G6PD-deficient erythrocytes, in steady-state conditions, have a low NADPH/NADP+ ratio, thus allowing the HMP to operate at its maximal intracellular rate and to compensate the intrinsic erythrocyte enzyme deficiency. Studies started soon after accidental intake of fava beans by sensitive G6PD-deficient subjects demonstrate a decrease of both NADPH/NADP+ ratio and reduced glutathione. The metabolic effects induced by fava beans may be attributed to oxidative stress probably associated with an inhibitor effect of some unknown metabolite on the HMP. The availability of erythrocytes from subjects recovering from haemolysis with high reticulocyte counts and increased G6PD activity, provides new information on the rate of synthesis as well as on the in vivo decay of the mutant enzyme. Correlation of G6PD activity to reticulocyte count and extrapolation to an ideally homogenous population of reticulocytes reveal that the mutant enzyme is synthesized at a nearly normal rate. Furthermore, the present correlation allows an estimate of the in vivo half-life of Mediterranean G6PD. The rate of decline of about 8 d observed in this study well correlates to the intracellular metabolic aspects of G6PD Mediterranean erythrocytes.

Artifacts imitating aging of glucose-6-phosphate dehydrogenase in human erythrocytes

Data in the literature based on the technique of graded osomotic hemolysis have been re-evaluated. Differences were previously found in the glucose-6-phosphate dehydrogenase/hemoglobin ratio and in the heat stability of the enzyme in hemolysates of 'old' and 'young' cells. These differences were believed to be due to the aging of the enzyme. As the erythrocyte membrane acts as a molecular sieve under hypotonic conditions [cf. Cseke, E., Váradi, A., Szabolcsi, G., and Biszku, E. (1978) FEBS Lett. 96, 15--18], the hemolysate obtained when a fraction is lysed does not properly represent the content of the lysed cells. As hemoglobin is lost from cells which are not yet lysed, the enzyme/hemoglobin ratio is underestimated in 'old' cells and overestimated in 'young' cells. It is further shown that the observed differences in the heat stability of glucose-6-phosphate dehydrogenase in the fractions obtained by graded hemolysis are due to the presence of different concentrations of endogeneous NADP. Therefore the published data obtained by graded osmotic hemolysis do not prove the assumption that the enzyme is aging during the lifetime of the erythrocyte.

Effects of hemolysate concentration, ionic strength and cytochrome b5 concentration on the rate of methemoglobin reduction in hemolysates of human erythrocytes

An assay for determining the rate of methemoglobin reduction in hemolysates of human erythrocytes has been developed. The rates obtained by this assay, when corrected for dilution, are comparable to those obtained with intact cells. Increased ionic strength inhibits the reaction, whereas EDTA increases the rate of reduction. The rate with NADPH as electron donor is 65-70% of the rate with NADH. Added cytochrome b5 stimulates the reaction. The assay has been used to examine erythrocytes from two methemoglobinemic sisters and their asymptomatic mother. Hemolysates of the two patients have both decreased dichlorophenolindophenol reductase activity and decreased ability to reduce methemoglobin. Hemolysates from the heterozygous mother have intermediate dichlorophenolindophenol reductase activity and intermediate methemoglobin reduction ability. The data presented in this paper indicate that the concentrations of cytochrome b5 and cytochrome b5 reductase determine the rate of methemoglobin reduction in hemolysates.

Guanosine triphosphate catabolism in human and rabbit erythrocytes: role of reductive deamination of guanylate to inosinate

The reductive deamination of guanylate to inosinate was demonstrable but occurred at low rates in human and rabbit erythrocytes incubated in vitro with or without glucose. However, the process was considerably accelerated in erythrocytes incubated with deoxyglucose. In human erythrocytes incubated with deoxyglucose, deamination was the major pathway of catabolism of guanylate; little or no guanylate was dephosphorylated. In rabbit erythrocytes, guanylate was both deaminated and dephosphorylated. Inosinate formed from guanylate was metabolized only by dephosphorylation in human erythrocytes, but in rabbit erythrocytes, it was also converted to xanthylate.

Effect of haemolysis on the hexose monophosphate pathway in normal and in glucose-6-phosphate dehydrogenase-deficient erythrocytes

The hexose monophosphate pathway of human glucose-6-phosphate dehydrogenase (EC 1.1.1.49) - deficient erythrocytes is under a severe and unexplained restraint (Gaetani, G.D., Parker, J.C. and Kirkman, H.N. (1974) Proc. Natl. Acad. Sci. U.S. 71, 3584-3587). In this study the hexose monophosphate pathway activity and the NADPH level of normal and glucose-6-phosphate dehydrogenase-deficient erythrocytes were measured soon after haemolysis. The results indicate a prompt increase in 14CO2 evolution and a rise in MADPH levels. Since, in this study, the concentration of the haemolysate is comparable to that of intact erythrocytes, the relief of the restraint on glucose-6-phosphate dehydrogenase through dilution-dependent dissociation from inactivator or inhibitor is excluded. The possibility that the intracellular restraint may result from compartmentalization of glucose-6-phosphate dehydrogenase and substrates or from properties of the intact membrane of the erythrocytes is suggested.

Glucose-6-phosphate dehydrogenase in vitro correlated with in vivo activity and reticulocytosis

In vitro activity of erythrocyte glucose-6-phosphate dehydrogenase (G-6-PD) does not always correlate with in vivo hemolytic manifestations. Many of these non-correlations are reviewed and can now be explained on the basis of altered substrate affinity and/or altered inhibition by intracellular metabolites. These alterations are not detected by standard assay conditions. The influence of a young erythrocyte population upon in vitro G-6-PD activity was determined and the lower limit of expected values shown to be raised at least to the mean of an average age erythrocyte population.

Studies on the mechanism of NADPH oxidation by the granule fraction isolated from human resting polymorphonuclear blood cells

Various factor affecting NADPH-oxidation by resting human leucocyte granules (LG) at acid pH, have been investigated. It was found that: 1) oxidation of NADPH by LG was increasingly inhibited by increased cyanide concentrations in the medium and was abolished by 4 mM cyanide. 2) with or without cyanide in the incubation medium, LG omitted, Mn++ in the presence of NADPH induced superoxide anion (O- WITH 2) production, as evidenced by oxygen consumption and H2O2 production, which were abolished (in the absence of cyanide) by cytochrome C (a potent O- with 2 scavenger). 3) Both NADPH oxidation in the presence of 2 mM cyanide (cyanide-resistant) and in its absence (cyanide-sensitive) by LG occurred only in the presence of Mn++, and both were inhibited by superoxide dismutase. 4) Cyanide-resistant NADPH oxidation by LG generated H2O2, was inhibited by H2O2 and was not modified by "active" catalase. The ratio of cyanide-resistant NADPH oxidation/O2 uptake was 1 up to 1.25 mM NADPH, and increased above this concentration. 5) Cyanide-sensitive NADPH oxidation was inhibited by catalase and increased upon addition of H2O2. The ratio of cyanide-sensitive NADPH oxidation/O2 uptake was 2. It was concluded that after initiation by O - with 2, produced independently of LG, two sequential types of LG dependent NADPH oxidations occur. First, an O - with 2-dependent protein mediated NADPH oxidation (cyanide-resistant) which generates H2O2 and O - with 2 occurs. Second, NADPH peroxidation (cyanide-sensitive) which utilizes H2O2 takes place.

Glucose-6-phosphate dehydrogenase Velletri

A new variant of red cell glucose-6-phosphate dehydrogenase (G6PD) has been found in a Caucasian man with congenital non-spherocytic haemolytic anaemia. This variant has reduced activity, increased thermolability, increased Michaelis constants for glucose-6-phosphate and NADP, slightly increased electrophoretic mobility, and a biphasic pH-activity profile. The red cell adenine compounds and ATP, are in normal limits. The increased activity of red cell NADP-glutathione reductase is probably the expression of a mechanism of compensation for the decrease of G6PD and a consequence of the decrease of NADPH.

Metabolism of (4-14C)estrone by sheep erythrocytes around the time of parturition

The metabolism of [4-14C]estrone in vitro by red blood cells of sheep in late pregnancy and after partuirition has been studied. [14C]estrone (600 ng) was incubated with 0.5 ml erythrocytes plus 0.5 ml of Krebs-Ringer phosphate buffer, pH 7.4, for 2 h at 37 degrees C in an atmosphere of air. After incubation, [3H]estrogens were added to the incubation medium as internal standards for identification and for correction for procedural losses. Metabolites were isolated and purified by chromatography, acetate derivative formation, and recrystallization to a constant 3H/14C ratio. Approximately 20% and 2% of added estrone were converted to 17beta-estradiol and 17 alpha-estradiol, respectively. The remainder was recovered unchanged. Daily measurements of 17 beta-hydroxysteroid dehydrogenase activity in erythrocytes of five ewes, over the period 8 days prepartum to 4 days postpartum, showed no significant change in activity.