Interaction of Haemoglobin with Ions

Berger, H.; Jänig, G.-R.; Gerber, Gerhard; Ruckpaul, K; Rapoport, S.

doi:10.1111/j.1432-1033.1973.tb03090.x

Cited by 77 publications

(43 citation statements)

References 37 publications

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“…The site is probably ATP which was found in the cells at a concentration of between 1-3 and 145 mm, (measured by the fire-fly assay, see Glynn & Hoffman, 1971). Under cellular conditions the dissociation constant for Mg-ATP is 0-083 mm (Berger et al 1973), whereas the calcium dissociation constant is about 0-217 mm (Collier & Lam, 1970). Hence the concentration and properties of the K1 system coincide closely with those of ATP.…”

Section: K1 Systemmentioning

confidence: 76%

“…The low affinity, high-capacity buffer is probably made up of a whole range of phosphate groups in the cell together with a small contribution from binding sites on amino acids and proteins. The major red cell constituent, haemoglobin, has been shown not to bind magnesium either in the oxygenated or deoxygenated state (Carr & Woods, 1955;Rose, 1968;Berger et al 1973). The total concentration of organic phosphate in the red cell is about 20 mm, of which 12 mm is contributed by 2,3-DPG, 4-5 mM by ATP and 3-5 mm by unspecified intermediates of the glycolytic and pentose shunt pathways (Deuticke, Duhm & Dierkesmann, 1971).…”

Section: K2 Systemmentioning

confidence: 99%

See 1 more Smart Citation

Magnesium buffering in intact human red blood cells measured using the ionophore A23187.

Flatman¹,

Lew²

1980

The Journal of Physiology

109

119

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SUMMARY1. A method was developed for measuring the cytoplasmic magnesium buffering of intact red cells using the divalent cation selective ionophore A23187. Addition of A23187 to a suspension of red cells induces rapid equilibration of ionized magnesium across the cell membrane.2. Entry of magnesium into red cells is associated with cell swelling and depolarization of the membrane potential.3. At an external ionized magnesium concentration of about 0-15 mm corresponding to an internal ionized concentration of 0-4 mm the addition of A23187 did not produce a change in the magnesium content of the cells. This indicates that the normal ionized magnesium concentration inside the oxygenated red cell is about 0-4 mM.4. The magnesium buffering curve for oxygenated, inosine-fed human red blood cells is adequately described by the existence of three buffer systems of increasing capacity and decreasing affinity. These are 0-15 mm with a Km < 10-7 M, probably structural magnesium bound within the cell proteins; 1-6 mm with a Km 0-08 mM, mainly ATP and other nucleotides; and about 21-25 mm with a Km 3-6 mM, a

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Section: K1 Systemmentioning

confidence: 76%

Section: K2 Systemmentioning

confidence: 99%

Magnesium buffering in intact human red blood cells measured using the ionophore A23187.

Flatman¹,

Lew²

1980

The Journal of Physiology

109

119

View full text Add to dashboard Cite

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“…The K,,, for the MgATP complex is 1 . 2~ lo4 M-l for pH 7.2; I = 0.15 a t 37 "C [5], as can be derived from the data given by Phillips et al [28]. If the conditions regarding pH, ionic strength and temperature are not to be changed the use of an overall-K,,, might be preferable, since all the individual species (MgATP2-, MgHATP1-, ATP4-, HATP3-, KATP3-, NaATP3-) vary proportionally to each other.…”

Section: Discussionmentioning

confidence: 99%

Hexokinase of Human Erythrocytes

Gerber

Preissler

Heinrich

et al. 1974

European Journal of Biochemistry

Self Cite

103

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Hexokinase was purified 680-fold from erythrocytes of man. The preparation was not contaminated by other glycolytic enzymes.Initial reaction rate measurements were performed at pH 7.2, ionic strength 0.15 and 37 "C by use of coupled optical assays. The experimental data were used to construct a kinetic model of the enzyme, the kinetic parameters of which were estimated by means of a computer-fit program.The hexokinase of erythrocytes operates by a rapid-equilibrium random mechanism. The dissociation constant of the E . glucose complex is 0.038 to 0.054 mM, of the F, -MgATP complex 1.0 to 2.1 mM. Uncomplexed Mg2+ up to 4 mM is capable of activating the enzyme velocity twofold (Knrgl+ = 1.0 mM). An inhibition was observed a t higher Mg2+ concentrations. a-D-Glucose 6-phosphate and &-D-glUCoSe 1,6-bisphosphate inhibit the hexokinase competitive to MgATP with dissociation constants of 0.069 mM. The enzyme is also inhibited by 2,3-bisphosphoglycerate competitive with respect to MgATP with a K P~G = 2.7 mM. An inhibition by uncomplexed ATP was not detected. The parameters of the kinetic model of the enzyme in conjunction with the free intracellular Concentrations of substrates and effectors were used to calculate the actual intracellular activity of the hexokinase in dependence on variations of pH, temperature and the state of haemoglobin oxygenation. The calculated hexokinase activities correspond to the glycolytic flux in all conditions considered, except a t pH 8.

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“…Therefore, the observed reduction cannot be attributed to pH. It is well documented that deoxygenation causes significant changes in [Mg2"], and [Mg2`]j/[ATP]1 (Berger, Janig, Gerber, Ruckpaul & Rapoport, 1973;Flatman, 1980;, which, in turn, can influence the Na+-K+-ATPase and Ca2+-Mg2+-ATPase as well as the active and passive ion transport functions of the red cell membrane b; Flatman & Lew, 1981;Flatman, 1988;Ortiz, Lew & Bookchin, 1990 (Lew et al 1982 We wish to thank the Wellcome Trust (UK) and the NIH (USA, Grants HL28018 and HL21016) for funds, Dr J. E. Raftos for helpful comments, and Mrs A. Gray for excellent technical assistance.…”

Section: Effect Of Deoxygenation On the Pl Of Hbmentioning

confidence: 99%