Bisphosphoglycerate mutase and pyruvate kinase activities during maturation of reticulocytes and ageing of erythrocytes

The relationship between plasma vascular endothelial growth factor and erythrocyte 2,3-bisphosphoglycerate: The putative role of chronic hypoxia

The non-invasive assessment of chronic tissue hypoxia is difficult. Pulse oximetry only allows the peripheral oxygen saturation to be measured, while the detection of hyperlactataemia needs to take into account the fact that the accumulation of lactic acid may result from several causes other than prolonged tissue hypoxia. Arterial blood oxygen measurement is invasive and often does not give a good indication of the level of tissue hypoxia. Other suggested methods include the use of positron emission tomography, magnetic resonance T₂^∗ relaxation time measurement, photoacoustics and high-frequency ultrasound. Tissue hypoxia leads to increased levels of hypoxia-inducible factor-1α, which in turn upregulates VEGFA, leading to increased levels of vascular endothelial growth factor (VEGF), which promote angiogenesis. Hypoxia lasting for more than a few hours is associated with increased synthesis in erythrocytes of 2,3-bisphosphoglycerate (BPG), a powerful regulator of the allosteric properties of haemoglobin, via the Rapoport-Luebering phosphoglycerate cycle. We therefore hypothesised that plasma VEGF and erythrocyte BPG levels should be positively correlated. Venous blood samples from 34 patients (18 male, mean age (standard error) 43.4 (3.2) y) were analysed; plasma VEGF was measured using an enzyme-linked immunosorbent assay while the erythrocyte BPG was assessed by quantitative Fourier transform infrared spectrometry following gel electrophoresis. The Pearson product-moment correlation between the two variables was 0.622 (p < 0.0001). Based on our findings, we suggest that it may be useful to measure both erythrocyte BPG and plasma VEGF, together, when assessing chronic hypoxia; elevated levels of both are likely to indicate hypoxia.

Human pyruvate kinase M2: a multifunctional protein

Glycolysis, a central metabolic pathway, harbors evolutionary conserved enzymes that modulate and potentially shift the cellular metabolism on requirement. Pyruvate kinase, which catalyzes the last but rate-limiting step of glycolysis, is expressed in four isozymic forms, depending on the tissue requirement. M2 isoform (PKM2) is exclusively expressed in embryonic and adult dividing/tumor cells. This tetrameric allosterically regulated isoform is intrinsically designed to downregulate its activity by subunit dissociation (into dimer), which results in partial inhibition of glycolysis at the last step. This accumulates all upstream glycolytic intermediates as an anabolic feed for synthesis of lipids and nucleic acids, whereas reassociation of PKM2 into active tetramer replenishes the normal catabolism as a feedback after cell division. In addition, involvement of this enzyme in a variety of pathways, protein-protein interactions, and nuclear transport suggests its potential to perform multiple nonglycolytic functions with diverse implications, although multidimensional role of this protein is as yet not fully explored. This review aims to provide an overview of the involvement of PKM2 in various physiological pathways with possible functional implications.

Effects of thyroid hormone and hypoxia on 2,3-bisphosphoglycerate, bisphosphoglycerate synthase and phosphoglycerate mutase in rabbit erythroblasts and reticulocytes in vivo

OBJECTIVES

The effects of triiodothyronine (T(3)) and hypoxia on 2,3-bisphosphoglycerate (2,3-BPG) studied in vitro are unclear. To clarify these effects we selected a more physiologic approach: the in vivo study in rabbits. We also present the changes produced by T(3) and hypoxia on phosphoglycerate mutase (PGAM), which requires 2,3-BPG as a cofactor, and 2,3-BPG synthase (BPGS), the enzyme responsible for 2,3-BPG synthesis in erythroblasts and reticulocytes.

METHODS

Hyperthyroidism was induced by daily T(3) injection (250 microg/kg), hypoxia by a mixture of 90% nitrogen and 10% oxygen and hypothyroidism by propylthiouracil (PTU) added to drinking water.

RESULTS

Both T(3) administration and hypoxic conditions increased 2,3-BPG levels and BPGS mRNA levels and activity in erythroblasts but not in reticulocytes. Unlike BPGS, both PGAM mRNA levels and activity were increased in erythroblasts and reticulocytes under hyperthyrodism and hypoxia. The antihormone PTU produced opposite effects to T(3).

CONCLUSION

The results presented here suggest that both hyperthyroidism and hypoxia modulate in vivo red cell 2,3-BPG content by changes in the expression of BPGS. Similarly, the changes in PGAM activity are also explained by changes in its expression.

Surface and metabolic properties of microcytic and macrocytic human anaemic red blood cells detected in polymer aqueous two-phase systems

Microcytic and macrocytic red blood cells from anaemic patients have been fractionated as a function of cell surface properties by the countercurrent distribution technique using charge-sensitive dextran/poly(ethylene glycol) aqueous two-phase systems. As deduced from the fractionation profiles, microcytic cells constitute a heterogeneous cell population with decreased surface charge properties while. macrocytic cells constitute a homogeneous cell population with behaviour similar to that of the control red blood cells. The specific activity of pyruvate kinase, an age-dependent enzyme, did not change along microcytic red blood cells fractionation profiles, suggesting that such cells have altered ageing properties. However, pyruvate kinase specific activity decreases from the left- to the right-hand side of the fractionation profile of macrocytic red blood cells, indicating that these cells follow the normal ageing process. Bisphosphoglycerate mutase specific activity did not change along the fractionation profile of any cell population under study, thus providing 2,3-bisphosphoglycerate during the life-span of the red blood cells from anaemic patients.

Surface properties of crosslinked erythrocytes as studied by counter-current distribution in aqueous polymer two-phase systems

The bifunctional imidoester dimethyl suberimidate hydrochloride can stabilize rat red blood cells (RBCs) by membrane protein crosslinking, and in that way they can be used as carrier systems for exogenous substances. Counter-current distribution fractionation in charge-sensitive dextran-polyethyleneglycol two-phase systems has been used to detect slight changes in surface charge in stabilized cells. A decrease in the surface charge of crosslinked RBCs and an apparent masking of the age-related cell surface properties have been found to result from the protein crosslinking. Digitonin treatment used to permeabilize crosslinked RBCs produces a significant decrease of the cell surface charge while the age-related surface properties do not seem to be modified by the treatment.

Transferrin binding capacity as a marker of differentiation and maturation of rat erythroid cells fractionated by counter current distribution in aqueous polymer two-phase systems

Rat bone marrow cell populations, containing different proportions of erythroid cells, have been fractionated by counter-current distribution in the non-charge-sensitive dextran/polyethyleneglycol two-phase systems on the basis of hydrophobic cell surface properties. Cell fractions with a low distribution coefficient, which contain non-erythroid cells and early erythoblasts, showed a low transferrin binding capacity and a low haemoglobin/cell ratio whereas cell fractions with a high distribution coefficient, which contain intermediate-late erythroblasts and mature red cells, showed an elevated transferrin binding capacity and the highest haemoglobin/cell ratio. These results support transferrin binding capacity as a good marker parameter for the erythroid bone marrow cell differentiation and maturation processes.

Biochemical characterization of human erythrocytes fractionated by counter-current distribution in aqueous polymer two-phase systems

The fractionation of normal human erythrocytes by counter-current distribution (CCD) in charge-sensitive dextran-polyethylene glycol two-phase systems was confirmed and extended to red blood cells from heterozygous beta-thalassaemic patients. The differences between the distribution profiles of normal (homogeneous) and abnormal (heterogeneous) red blood cells reflect their different surface-charge properties. As suggested by the decline of membrane sialic acid released after neuraminidase treatment and the specific activities of two age-dependent enzymes (membrane acetylcholinesterase and intracellular pyruvate kinase) in the distribution profiles (from the left- to the right-hand side fractions), the fractionation seems to be according to red blood cell age. A constancy of the 2,3-bisphosphoglycerate level was observed in ageing red blood cells.

Rat bone marrow erythroid cell fractionation by counter current distribution in non-charge-sensitive two-phase systems

Counter-current distribution in non charge-sensitive aqueous poly(ethylene glycol)-dextran two phase systems allows the fractionation of rat bone marrow cells into two broad cell subpopulations with different distribution coefficients in a relatively short time. Morphological identification and enzymatic studies suggest that erythroid cells are mainly present in the subpopulation with the higher distribution coefficient. The distribution coefficient and, therefore, surface hydrophobicity of these cells, apparently increase in parallel with an increase in their degree of differentiation and maturation.

Changes in glycolytic enzyme activities in aging erythrocytes fractionated by counter-current distribution in aqueous polymer two-phase systems

Human and rat erythrocytes were fractionated by counter-current distribution in charge-sensitive dextran/poly(ethylene glycol) two-phase systems. The specific activities of the key glycolytic enzymes (hexokinase, phosphofructokinase and pyruvate kinase) declined along the distribution profiles, although the relative positions of the activity profiles were reversed in the two species. These enzymes maintained their normal response to specific regulatory effectors in all cell fractions. No variations were observed for phosphoglycerate kinase and bisphosphoglycerate mutase activities. Some correlations between enzyme activities (pyruvate kinase/hexokinase, pyruvate kinase/phosphofructokinase, pyruvate kinase/pyruvate kinase plus phosphoglycerate kinase, pyruvate kinase/bisphosphoglycerate mutase and phosphoglycerate kinase/bisphosphoglycerate mutase ratios) were studied in whole erythrocyte populations as well as in cell fractions. These results strongly support the fractionation of human erythrocytes according to cell age, as occurs with rat erythrocytes.

Increase of 2,3-bisphosphoglycerate synthase/phosphatase during maturation of reticulocytes with high 2,3-bisphosphoglycerate content

In the rabbit and in the rat, which possess erythrocytes with high concentration of 2,3-bisphosphoglycerate, the 2,3-bisphosphoglycerate synthase activity increases more than two fold during reticulocyte maturation. Isolation of the enzymes with 2,3-bisphosphoglycerate synthase activity present in extracts of reticulocytes and mature erythrocytes by ion exchange fast liquid chromatography shows that the increase in the synthase activity is due to the accumulation of the bifunctional enzyme 2,3-bisphosphoglycerate synthase/phosphatase (EC2.7.5.4/EC3.1.3.13) which represents more than 80% of the synthase activity of the cell extracts. During reticulocyte maturation phosphoglycerate mutase (EC 5.4.2.1), which makes a small contribution to the 2,3-bisphosphoglycerate synthase activity in the erythroid cells, decreases in the rabbit and remains constant in the rat.

Fractionation in two-phase systems of red cells during rat development: changes in pyruvate kinase and bisphosphoglycerate mutase activities in relation to red cell switching

An inverse relationship between 2,3-bisphosphoglycerate levels and the ratio calculated from pyruvate kinase and bisphosphoglycerate mutase activities has been observed in red populations of rats during animal development. Counter-current distribution in aqueous two-phase systems of these cells populations shows a displacement of distribution profiles towards the high-numbered cavities of the rotor as animal ages. Heterogeneity of cells after distribution is only observed during the switching process from fetal to adult red cells taking place along the postnatal stage of development. Values for the pyruvate kinase/bisphosphoglycerate mutase ratio in these fractions suggest the separation of fetal (liver) from adult (bone marrow) red cells.

Analysis by partitioning in aqueous two-phase systems of the loss of transferrin-binding capacity during maturation of rat reticulocytes

A decrease in the number of binding sites for 125I-transferrin, without an apparent modification of the association constant, has been observed during the maturation of reticulocytes into erythrocytes. As an experimental model, different red cell populations from phenylhydrazinic anaemic rates (95% to 12% reticulocyte-rich) have been used. The fractionation by multiple partition in two-phase systems of these red cell populations has been applied here to show the relationship between number of transferrin receptors and rate of reticulocyte maturation.