Glucose-6-phosphate dehydrogenase (G6PD) iserlohn and G6PD regensburg: Two new severe enzyme defects in german families

Summary Two new inheritable variants of glucose-6-phosphate dehydrogenase have been found in two unrelated German families. Patients with one variant (G6PD Iserlohn, also referred to as G6PD I) suffered from intermittent hemolytic crises caused by fava beans; patients with the other variant (G6PD Regensburg, G6PD II) disclosed chronic nonspherocytic hemolytic anemia aggravated by drug treatment. Due to their unusual biochemical characteristics, the new variants were designated G6PD Iserlohn and G6PD Regensburg. Both variants showed a reduction of enzyme activity to about 6% of the normal in erythrocytes, normal electrophoretic mobility, increased affinity for glucose-6-phosphate, a reduced affinity for NADP and a pH optimum in the neutral region (7.0 and 7.5). G6PD Iserlohn had a decreased affinity for the inhibitor NADPH; G6PD Regensburg had a normal inhibitor constant. Deamino NADP was utilized at an increased rate by G6PD Regensburg. G6PD Iserlohn was thermostable, G6PD Regensburg mildly instable. G6PD activity in leukocytes was normal in G6PD Iserlohn and reduced to the same degree as in erythrocytets in G6PD Regensburg. The cause of the decreased activity of G6PD Iserlohn appears to be in vivo instability; in G6PD Regensburg further mechanisms might include reduced specific activity or reduced synthesis of the variant enzyme.     

A Contradiction Between in vivo and in vitro Activities of Normal and Variant Glucose 6-Phosphate Dehydrogenase

The presumed “physiologic activity” of normal glucose 6-phos-phate dehydrogenase (G6PD), i.e. activity assayed in the presence of physiologic concentrations of ATP, 2,3-diphosphoglycerate, glucose 6-phosphate, NADP and NADPH in the normal red cells, is comparable to shunt pathway activity of intact normal red cells. In contrast, the presumed “physiologic activity” of G6PD variants associated with enzyme deficiency (Gd A® and Gd Mediterranean) is one order of magnitude higher than actual shunt pathway activity of the variant red cells. The difference of kinetic parameters of the enzyme in artificial buffer media and presumed physiologic medium in red cells cannot explain the discrepancy. The apparent discrepancy could be attributed either to (a) over-estimation of NADP and under-estimation of NADPH concentrations in the G6PD deficient red cells due to rapid oxidation of NADPH to NADP in preparation of hemolysate, or to (b) a large portion of NADP which accumulated in the G6PD deficient red cells binds with cellular components of intact red cells and is not available as substrate for G6PD.

Whatever the mechanisms are, the balance of NADP and NADPH is a major factor for regulating shunt pathway activity, and the sensitivity of NADPH inhibition (i.e. K_m for NADP versus K_i for NADPH) can be considered as an important factor in differentiating hemolytic severity of several Gd variants.     

Two new glucose-6 phosphate dehydrogenase (G6PD) variants associated with hemolytic anemia: G6PD Amman-1 and G6PD Amman-2

Two glucose-6-phosphate dehydrogenase (G6PD) variants were investigated. G6PD Amman-1 was partially purified from the red cells of a patient suffering from recurrent jaundice and spontaneous episodic attacks of severe hemolysis in the absence of oxidant drugs, infection, or fava beans. The enzymatic characteristics of G6PD Amman-1 were markedly reduced activity, fast eletrophoretic mobility, slightly increased km for NADP, normal km for G-6-P, normal heat stability, normal utilization of substrate analogues 2-deoxy G-6-P and deamino-NADP, and a monophasic pH curve with a peak at 8.5 to 9.3. The second variant, G6PD Amman-2, was partially purified from the red cells of a patient suffering from recurrent jaundice with episodic mild hemolysis caused by infection or unknown factors. G6PD Amman-2 characteristics were severely reduced activity, slow electrophoretic mobility, normal km for NADP, decreased km for G-6-P, decreased heat stability, increased utilization of substrate analogues, and a monophasic pH curve with a narrow peak at pH 9.5. The red cell level of reduced glutathione was markedly decreased with twofold increase in the activity of glutathione reductase in the patient with G6PD Amman-2.     

A Philippino Glucose-6-Phosphate Dehydrogenase Variant (G6PD Union) With Enzyme Deficiency and Altered Substrate Specificity

A variant of glucose-6-phosphate dehydrogenase (G6PD) associated withaltered substrate specificity and severe deficiency of red cell enzyme activitywas found in a Philippino male and in his relatives. The genetic pattern wasconsistent with X-linked inheritance. -Thalassemia was found in the propositusand in several family members, but there was no interaction between G6PDdeficiency and -thalassemia. This G6PD variant has two pH optima, at pH5.5 and pH 9.0, while the normal enzyme is inactive at pH 5.5. The substratespecificity of the variant enzyme is different from any known G6PD variant:2-deoxyglucose-6-phosphate and galactose-6-phosphate are good substrates anddeamino-NADP is a better coenzyme than NADP. Although G6PD activityin the variant red cells was only three per cent of normal, quantitative immunologic neutralization suggested that the specific activity of the variantenzyme might be at least ten per cent of that of the normal enzyme. Thisvariant is named after the place of origin, Gd Union.

Submitted on August 11, 1969 Accepted on October 31, 1969     

Haemolytic Anaemia due to Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency: Demonstration of Two New Biochemical Variants, G6PD Hamm and G6PD Tarsus

Two new variants of erythrocytic glucose-6-phosphate dehydrogenase have been found in one German patient and in another patient of Turkish origin. The enzymes were partially purified 165-fold and 111-fold respectively. Both revealed reduced activity, increased thermolability and a pH-optimum in the alkaline region (8.5 and 9.0). One variant (G6PD Hamm) had a low Km-value for glucose-6-phosphate, the other (G6PD Tarsus) exhibited an increased affinity for glucose-6-phosphate and a reduced affinity for NADP+. This enzyme showed an increased inhibitor constant for NADPH with respect to NADP+. Electrophoretic mobility was normal in both cases. 2-Desoxy glucose-6-phosphate was utilized to an increased rate by both variant enzymes (46% and 33%). Also galactose-6-phosphate (29% and 25%) and deamino-NADP+ (230% and 261%) gave increased utilization rates. The mothers of both patients could be identified as heterozygous for this enzyme deficiency.     

A New Variant of Glucose-6-Phosphate Dehydrogenase Deficiency Hereditary Hemolytic Anemia, G6PD Cornell: Erythrocyte, Leukocyte, and Platelet Studies

A variant of glucose-6-phosphate-dehydrogenase deficiency associated withchronic hereditary hemolytic anemia wasdiscovered in a 9-yr-old white male. Theerythrocytes contained 5% of normalenzyme activity, the Km NADP was twoto three times normal, the pH optimumwas decreased, and the heat stabilitywas markedly decreased. The Km G6PD,electrophoretic mobility (B), and utilization of substrate analogues 2-deoxy-G6Pand deamino-NADP were normal. Theactivity of G6PD in the leukocytes andplatelets was 15% and 28% of normalvalues, respectively, but bactericidal activity and platelet function were unaffected by the deficiency of G6PD.

Submitted on September 10, 1973 Accepted on March 8, 1974     

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.     

G-6-PD Long Prairie: a new glucose-6-phosphate dehydrogenase mutant exhibiting normal sensitivity to inhibition by NADPH and accompanied by nonspherocytic hemolytic anemia.

The enzymatic properties of a new glucose-6-phosphate dehydrogenase (G-6-PD) variant (G-6-PD Long Prairie) were studied in a white patient with chronic nonspherocytic hemolysis. The red cells were found to have 2.3%-7.7% normal enzymatic activity. The mutant enzyme exhibited marked heat instability, an increased pH optimum, a moderately decreased Km for G-6-P, and increased utilization of 2-deoxyglucose-6-phosphate and deamino NADP. The Km for NADP and Ki for NADPH were both normal. G-6-PD Long Prairie is an interesting new G-6-PD variant that demonstrates that chronic hemolysis can be associated with modestly decreased G-6-PD activity despite normal sensitivity to inhibition by NADPH. Although increased sensitivity to inhibition by NADPH has been postulated to decrease intracellular enzyme activity, resulting in enhanced susceptibility to hemolysis in certain G-6-PD variants with only moderately decreased enzymatic activity, an alternative mechanism of hemolysis, possibly enzyme thermolability, exists in G-6-PD Long Prairie.     

Biochemical and molecular characterization of a new sporadic glucose-6-phosphate dehydrogenase variant described in Italy: G6PD Modena

Summary. A new glucose-6-phosphate dehydrogenase variant detected in an Italian man from the Po delata is described and designated as G6PD Modena. Biochemical characterization of the variant enzyme revealed an activity 21% of normal, a slow electrophoretic mobility, increased K_m value for NADP, decreased K_m value for G6P and a complete absence of NADPH inhibition, which could account for the apparently nonhaemolytic feature of this variant. The cloning and sequencing of the G6PD Modena allele showed a GC transition at nucleotide 844 in exon VIII causing a Asp His amino acid substitution. On the basis of biochemical characterization, G6PD Modena is classified as a genuine variant but it has the same mutation as G6PD Seattle-like.     

Modifications of purified glucose-6-phosphate dehydrogenase and other enzymes by a factor of low molecular weight abundant in some leukemic cells.

Highly purified platelet glucose-6-phosphate dehydrogenase (G6PD; D-glucose-6-phosphate:NADP+ 1-oxidoreductase, EC 1.1.1.49) can be modified in its isoelectric point and its molecular specific activity by extracts of some leukemic granulocytes. The "G6PD modifying factors" are relatively small molecules (molecular weight slightly under 5000), thermostable, dialyzable, and ultrafilterable. These molecules are destroyed by various endo- and exopeptidases and by serine enzymes present in crude extracts of leukocytes and commercial preparations of ribonuclease. The alterations of platelet G6PD due to the "G6PD modifying factors" are stable and not reversible by dialysis or further chromatography. The leukemic extracts which are able to modify G6PD also can modify the electrophoretic mobility and (or) the enzymatic activity of purified leukocyte pyruvate kinase, 6-phosphogluconate dehydrogenase, and glucosephosphate isomerase. The chemical nature of such modifications and their relationships with post-translational modifications which occur in leukemic or normal cells are discussed.     

Four new electrophoretically slow-moving glucose 6-phosphate dehydrogenase variants associated with congenital nonspherocytic hemolytic anemia found in Japan: Gd(-) Kurume,Gd(-) Fukushima,Gd(-) Yamaguchi and Gd(-) Wakayama

Four new glucose 6-phosphate dehydrogenase (G6PD) variants which had electrophoretically slow-moving characteristics associated with congenital nonspherocytic hemolytic anemia were discovered in Japan. Gd(-) Kurume was found in a 17-year-old male whose red cells contained only 0.8% of normal enzyme activity. Gd(-) Kurume had a normal Km G6P, normal Km NADP, low Ki NADPH, normal utilization of 2-deoxy-G6P and deamino-NADP, very low heat stability and a biphasic pH curve. The hemolytic anemia was mild. Gd(-) Fukushima was characterized from a 33-year-old male and had 2.8% of normal enzyme activity, normal Km G6P, normal Km NADP, low Ki NADPH, normal utilization of 2-dcoxy-G6P, low utilization of deamino-NADP, low heat stability and a normal pH curve. The hemolytic anemia was mild. Gd(-) Yamaguchi was characterized from an 8-year-old boy and had 3.5% of normal enzyme.     

Combined glucose-6-phosphate dehydrogenase and glucosephosphate isomerase deficiency can alter clinical outcome

Glucosephosphate isomerase (GPI) deficiency in humans is an autosomal recessive disorder, which results in nonspherocytic hemolytic anemia of variable clinical expression. A 4-year-old female with severe congenital hemolytic anemia had low red cell GPI activity of 15.5 IU/g Hb (50% of normal mean) indicating GPI deficiency. Subsequent DNA sequence analysis revealed a novel homozygous 921C to G mutation in the GPI gene sequence, predicting a Phe307 to Leu replacement. Strikingly, the red cell GPI activity in this patient was higher than that found in a second patient expressing the same GPI variant, with a more severe clinical phenotype. We propose that the hemolysis in the first patient may be modified by an accompanying deficiency of glucose-6-phosphate dehydrogenase (G6PD). The proband's red cell G6PD activity was reduced at 4.5 IU/g Hb (50% of normal mean) and molecular studies revealed heterozygosity for the G6PD Viangchan mutation and a skewed pattern of X-chromosome inactivation, producing almost exclusive expression of the mutated allele. The G6PD Viangchan variant is characterised by severe enzyme deficiency, but not chronic hemolysis. This study suggests that the metabolic consequences of a combined deficiency of GPI and G6PD might be responsible for a different clinical outcome than predicted for either defect in isolation.     

G6PD Napoli and Ferrara II: Two New Glucose-6-Phosphate Dehydrogenase Variants having Similar Characteristics but Different Intracellular Lability and Specific Activity

S ummary. Two new glucose-6-phosphate dehydrogenase (G6PD, d -glucose 6-phosphate: NADP oxido reductase, E.C. 1.1.1.49) variants, designated G6PD Napoli and G6PD Ferrara II, are described in propositi from two unrelated families. Characterization side by side of the two variants according to W.H.O. recommendations reveals minor differences which are mostly related to utilization of artificial substrates (increased in both cases as compared with normal G6PD type B). Other properties, which are not significantly distinctive between the two variants, are an enzyme activity amounting to nearly 20% of normal, a decreased electrophoretic mobility, decreased K _m values for glucose-6-phosphate and NADP, normal thermostability and biphasic pH curves. However, marked differences emerged between the two variants and between either variant and G6PD B as well, when a number of microtechniques were used. These were: (1) the half-lives of G6PD Napoli and G6PD Ferrara II are 16 and 29 d, respectively, while that of G6PD B is 63 d; (2) the specific activities, measured by a method involving direct estimation of G6PD protein on sodium dodecyl sulphate polyacrylamide gel electrophoretic tracings, are 166 I.U./mg (G6PD Napoli) and 59 I.U./mg (G6PD Ferrara II), as compared with normal value of 180 I.U./mg (G6PD B). On the whole, these findings allow the conclusion that the deficiency of catalytic activity is related to an accelerated though distinctive decay of both mutant enzyme proteins within the affected erythrocytes and that a significant impairment of catalytic efficiency is also involved, as a result of the underlying structural mutation in the case of G6PD Ferrara II.     

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.     

Redox and energetic state of red blood cells in G6PD deficiency, heterozygous beta-thalassemia and the combination of both

The levels of ATP, ADP, AMP, NADP, NADPH, NAD, NADH and reduced glutathione were determined in the red blood cells of individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency, beta-thalassemia (beta-thal) heterozygotes and in a boy carrying both mutations. The results obtained confirmed a reduced concentration of NADPH in G6PD deficiency and showed that with the combination of both diseases, the red blood cell contained practically undetectable levels of NADPH. Assays of some red blood cell enzyme activities known to be markedly influenced by cell age suggested that a younger mean red cell population is present in beta-thal/G6PD deficiency. Thus, the marked oxidative stress caused by beta-thal, that is apparently incompatible with G6PD deficiency, in fact exists, probably because of the residual activity of this enzyme in the younger red cells.     

Molecular basis of G6PD deficiency in India

G6PD deficiency has been reported from India more than 30 years ago and about 13 variants have been characterized biochemically. Here, we report the results of an epidemiological study investigating G6PD deficiency and the mutations among 14 heterogenous populations of India. Of the 3166 males tested, 332 (10.5%) were found to be G6PD-deficient and the prevalence rate varied from 5.7% to 27.9% in the different population groups. Molecular characterization revealed that G6PD Mediterranean (563 C-->T) was the commonest (60.4%) deficient variant followed by G6PD Kerala-Kalyan (949 G-->A; 24.5%) and G6PD Orissa (131 C-->G; 13.3%). G6PD Mediterranean had a more widespread distribution as compared to G6PD Kerala-Kalyan and G6PD Orissa and was associated with both 1311 C and 1311 T polymorhism. G6PD Mediterranean was found to have significantly lower red cell enzyme activity and more severe clinical manifestations than the other two. G6PD Chatham (1003 G-->A) with undetected red cell enzyme activity and G6PD Insuli (989 G-->A) with normal G6PD activity were very rare in the Indian population. The absence of a large number of mutations causing G6PD deficiency points to the fact that the genetic diversity of these populations is considerably lowered than expected.     

Glucose-6-phosphate dehydrogenase of malaria parasite Plasmodium falciparum

Plasmodium falciparum growth is impaired in glucose-6-phosphate dehydrogenase (G6PD)-deficient red blood cells (RBCs), and malaria has been implicated in the spreading of deficient variants in malaria- endemic areas. Recent reports suggest that the malaria parasite can adapt itself to grow in these variant RBCs by producing its own G6PD, but studies on parasite G6PD are very limited. In this report, we define the properties of the parasite G6PD. G6PD was partially purified from infected and uninfected variant RBCs associated with severe G6PD deficiency. G6PD from infected RBCs contained two components separable by starch gel electrophoresis: a major component (approximately 90% activity) with a very slow anodal electrophoretic mobility and a minor component (approximately 10% activity) with the same mobility as the host G6PD. Parasite G6PD exhibited much higher affinity (low Km) to G6P and nicotinamide-adenine dinucleotide phosphate (NADP) than did human G6PD. Southern blot hybridization indicated that the parasite genome contained nucleotide sequences that were hybridizable with the human G6PD cDNA. These data indicate that the parasite is capable of adapting to G6PD-deficient RBCs by producing its own G6PD.     

The adaptation of Plasmodium falciparum to oxidative stress in G6PD deficient human erythrocytes

It has recently been found that growth of P. falciparum in human G6PD deficient red cells is impaired in vitro; however, the inhibition is overcome after two or three growth cycles. There is evidence to suggest that the parasite can produce its own G6PD enzyme which may compensate for the lack of host enzyme and could account for the resumption of normal growth in G6PD deficient host cells. It is unclear whether the parasite enzyme can enable the host cell to resist oxidative stress as normal cells do. To answer this question, P. falciparum was grown in vitro in: (a) normal red cells, (b) G6PD deficient red cells for one growth cycle only, (c) G6PD deficient cells for a minimum of five cycles. All groups were then challenged with acetylphenylhydrazine (APH) which served as an oxidative stress. Both G6PD (A-) and Mediterranean deficient types were studied. The results show a two-fold increase in resistance to oxidative stress by parasites adapted to G6PD-Mediterranean deficient host cells as compared to unadapted ones, but the parasite-red cell system remains 4 times more sensitive to APH than normal infected cells. In parasitized G6PD (A-) red cells, evidence of adaptation could be seen in the growth curves, but no detectable increase in resistance to APH was found in adapted parasites. It is concluded that the role of the parasite G6PD is not likely to be mainly related to oxidative stress resistance and therefore other functions of this enzyme should be investigated.     

Preparation of a monoclonal antibody to rat liver glucose-6-phosphate dehydrogenase and the study of its immunoreactivity with native and inactivated enzyme.

A monoclonal antibody of the IgG class was prepared against rat liver glucose-6-phosphate dehydrogenase (G6PD; D-glucose-6-phosphate:NADP+ 1-oxidoreductase, EC 1.1.1.49) by the hybridoma technique. This antibody does not affect the catalytic activity of the enzyme and shows crossreactivity with the palmitoyl CoA-inactivated G6PD. By solid phase radioimmunoassay, the presence of crossreacting materials in comparable amounts was determined in liver homogenate supernatants from rats that had been starved and refed a high-sucrose diet (containing a high level of G6PD activity) and from rats that had been starved and refed a high-fat diet (containing a low level of G6PD activity). These findings indicate that G6PD is present in an inactive form in rats fed a high-fat diet. The monoclonal antibody will facilitate isolation and characterization of the inactive variant G6PD.