scholarly journals The oxygen-linked zinc-binding site of human haemoglobin

1978 ◽  
Vol 169 (3) ◽  
pp. 625-632 ◽  
Author(s):  
J G Gilman ◽  
G J Brewer
Keyword(s):  
Binding Sites ◽  
Zinc Ion ◽  
Bohr Effect ◽  
Zinc Binding ◽  
Hill Coefficient ◽  
Human Haemoglobin ◽  
Equilibrium Binding ◽  
Zinc Binding Site ◽  
Alkaline Bohr Effect ◽  
The Hill

Zn2+ is known to increase the 02 affinity of human haemoglobin. Previous data suggested that Zn2+ exerts its effect by directly binding to haemoglobin, rather than by competing with or binding to 2,3-bisphosphoglycerate. It was also shown that there are two 02-linked zinc-binding sites in haemoglobin, and that Zn2+ does not significantly alter haemoglobin co-operativity or the alkaline Bohr effect. The effect of Zn2+ on 02 affinity of haemoglobin can also be observed for other haemoglobins as diverse as those of cow and chicken. This paper presents new data on the haemoglobin-zinc interaction for normal haemoglobin, des-His146beta-haemoglobin and N-ethylsuccinimide-haemoglobin of humans. For normal haemoglobin (0.05 mM in tetramers), at 20 degrees C in buffer containing 0.1 M-Cl-, 02-dissociation-curve experiments showed that the addition of 0.4-0.5 mM-ZnS04 did not change the Bohr effect between pH 6.71 and 7.29. Similar experiments, with “zinc-ion buffers”, showed that the value of the Hill coefficient, h, decreased only slightly if the concentration of free Zn2+ was held constant. For N-ethylsuccinimide-haemoglobin, Zn2+ caused less increase in O2 affinity than for normal haemoglobin. These studies, together with data on the equilibrium binding of Zn2+ to oxy-, deoxy- and des-His146beta-haemoglobins, suggest that zinc is chelated in oxyhaemoglobin by at least three amino acids, two of which are histidine-146beta and cysteine-93beta.

scholarly journals Crystal structure of the DENR-MCT-1 complex revealed zinc-binding site essential for heterodimer formation

2018 ◽  
Vol 116 (2) ◽  
pp. 528-533 ◽  
Author(s):  
Ivan B. Lomakin ◽  
Sergey E. Dmitriev ◽  
Thomas A. Steitz
Keyword(s):  
Crystal Structure ◽  
Binding Site ◽  
Translation Initiation ◽  
Zinc Ion ◽  
Zinc Binding ◽  
Ion Binding ◽  
Binding Interface ◽  
Zinc Binding Site ◽  
Reading Frames ◽  
Zinc Ion Binding

The density-regulated protein (DENR) and the malignant T cell-amplified sequence 1 (MCT-1/MCTS1) oncoprotein support noncanonical translation initiation, promote translation reinitiation on a specific set of mRNAs with short upstream reading frames, and regulate ribosome recycling. DENR and MCT-1 form a heterodimer, which binds to the ribosome. We determined the crystal structure of the heterodimer formed by human MCT-1 and the N-terminal domain of DENR at 2.0-Å resolution. The structure of the heterodimer reveals atomic details of the mechanism of DENR and MCT-1 interaction. Four conserved cysteine residues of DENR (C34, C37, C44, C53) form a classical tetrahedral zinc ion-binding site, which preserves the structure of the DENR’s MCT-1–binding interface that is essential for the dimerization. Substitution of all four cysteines by alanine abolished a heterodimer formation. Our findings elucidate further the mechanism of regulation of DENR-MCT-1 activities in unconventional translation initiation, reinitiation, and recycling.

scholarly journals The binding of carbon dioxide by horse haemoglobin

1971 ◽  
Vol 124 (1) ◽  
pp. 31-45 ◽  
Author(s):  
J. V. Kilmartin ◽  
L. Rossi-Bernardi
Keyword(s):  
Carbon Dioxide ◽  
Bohr Effect ◽  
Alkaline Ph ◽  
Amino Groups ◽  
Expected Number ◽  
Physiological Conditions ◽  
Alkaline Bohr Effect ◽  
Ph Range ◽  
The Hill ◽  
Β Chain

1. Three modified horse haemoglobins have been prepared: (i) αc2βc2, in which both the α-amino groups of the α- and β-chains have reacted with cyanate, (ii) αc2β2, in which the α-amino groups of the α-chains have reacted with cyanate, and (iii) α2βc2, in which the two α-amino groups of the β-chain have reacted with cyanate. 2. The values of n (the Hill constant) for αc2βc2, α2βc2 and αc2β2 were (respectively) 2.5, 2.0 and 2.6, indicating the presence of co-operative interactions between the haem groups for all derivatives. 3. In the alkaline pH range (about pH8.0) all the derivatives show the same charge as normal haemoglobin whereas in the acid pH range (about pH6.0) αc2βc2 differs by four protonic charges and αc2β2, α2βc2 by two protonic charges from normal haemoglobin, indicating that the expected number of ionizing groups have been removed. 4. αc2β2 and αc2βc2 show a 25% decrease in the alkaline Bohr effect, in contrast with α2βc2, which has the same Bohr effect as normal haemoglobin. 5. The deoxy form of αc2βc2 does not bind more CO2 than the oxy form of αc2βc2, whereas αc2β2 and α2βc2 show intermediate binding. 6. The results reported confirm the hypothesis that, under physiological conditions, haemoglobin binds CO2 through the four terminal α-amino groups and that the two terminal α-amino groups of α-chains are involved in the Bohr effect.

scholarly journals Allosteric effects of Mg2+ on the gating of Ca2+-activated K+ channels from mammalian skeletal muscle

1986 ◽  
Vol 124 (1) ◽  
pp. 5-13
Author(s):  
J. Golowasch ◽  
A. Kirkwood ◽  
C. Miller
Keyword(s):  
Binding Sites ◽  
Hill Coefficient ◽  
K Channel ◽  
Activation Process ◽  
Mammalian Skeletal Muscle ◽  
Activation Curve ◽  
K Channels ◽  
The Hill ◽  
Cytoplasmic Side ◽  
High Conductance

Ca2+-activated K+ channels from rat muscle transverse tubule membranes were inserted into planar phospholipid bilayers, and the activation of these channels by Ca2+ was studied. On the cytoplasmic side of the channel, calcium ions (in the range 10–100 mumol l-1) increase the opening probability of the channel in a graded way. This ‘activation curve’ is sigmoid, with an average Hill coefficient of about 2. Magnesium ions, in the range 1–10 mmol l-1, increase the apparent affinity of the channel for Ca2+ and greatly enhance the sigmoidicity of the Ca2+ activation curve. In the presence of 10 mmol l-1 Mg2+, the Hill coefficient for Ca2+ activation is about 4.5. This effect depends upon Mg2+ concentration but not upon applied voltage. Mg2+ is effective only when added to the cytoplasmic side of the channel. The results argue that this high-conductance, Ca2+-activated K+ channel contains at least six Ca2+-binding sites involved in the activation process.

scholarly journals Histidine residues of zinc ligands in β-lactamase II

1978 ◽  
Vol 175 (2) ◽  
pp. 441-447 ◽  
Author(s):  
G S Baldwin ◽  
A Galdes ◽  
H A O Hill ◽  
B E Smith ◽  
S G Waley ◽  
...  
Keyword(s):  
Bacillus Cereus ◽  
Binding Site ◽  
Binding Sites ◽  
Zinc Binding ◽  
Histidine Residue ◽  
Beta Lactamase ◽  
Histidine Residues ◽  
Zinc Enzyme ◽  
Zinc Binding Site ◽  
Ph Range

1. The Zn(II)-requiring beta-lactamase from Bacillus cereus 569/H/9, which has two zinc-binding sites, was examined by 270 MHz 1H n.m.r. spectroscopy. Resonances were assigned to five histidine residues. 2. Resonances attributed to three of the histidine residues in the apoenzyme shift on the addition of one equivalent of Zn(II). 3. Although these three histidine residues are free to titrate in the apoenzyme, none of them titrates over the pH range 6.0–9.0 in the mono-zinc enzyme. 4. The ability of the C-2 protons of these three histidine residues to exchange with solvent (2H2O) is markedly decreased on Zn(II) binding. 5. It is proposed that these three histidine residues act as zinc ligands at the tighter zinc-binding site. 6. Resonances attributed to a fourth histidine residue shift on addition of further zinc to the mono-zinc enzyme. It is proposed that this histidine residue acts as a Zn(II) ligand at the second zinc-binding site.

A comparative study of the activation of the cholinergic receptor by various agonists

1983 ◽  
Vol 218 (1211) ◽  
pp. 241-251 ◽  
Keyword(s):  
Dose Response ◽  
Binding Sites ◽  
Nicotinic Receptor ◽  
Response Curve ◽  
Cholinergic Receptor ◽  
Hill Coefficient ◽  
Frog Neuromuscular Junction ◽  
Cholinergic Agonists ◽  
The Mean ◽  
The Hill

At the frog neuromuscular junction, a dose-response curve for the activation of the nicotinic receptor by carbachol has been determined under conditions where desensitization could be estimated and corrected for. The value of the Hill coefficient was 2 and that of the dissociation constant for carbachol was 400 μm, the two binding sites of the receptor being assumed identical. The properties of six cholinergic agonists were then compared. The potencies and mean open times of these agonists are ranked in the same order, but the range of the potencies is much larger (1–200) than that of the mean open times (1-4). The differences in the properties of the different agonists could simply be due to differences in the rate of dissociation of the agonist, if it is assumed that one apparent opening of the channel is in fact a burst of several oscillations between the open and closed conformations, such that a burst is interrupted by the dissociation of one agonist molecule.

scholarly journals Kinetic Characterisation of Phosphofructokinase Purified from Setaria cervi: A Bovine Filarial Parasite

2011 ◽  
Vol 2011 ◽  
pp. 1-10 ◽  
Author(s):  
Bechan Sharma
Keyword(s):  
Adult Female ◽  
Binding Sites ◽  
Inhibitory Concentration ◽  
Product Inhibition ◽  
Hill Coefficient ◽  
Enzyme Protein ◽  
Setaria Cervi ◽  
The Hill ◽  
Inhibition Studies ◽  
Cooperative Kinetics

Phosphofructokinase (PFK), a regulatory enzyme in glycolytic pathway, has been purified to electrophoretic homogeneity from adult female Setaria cervi and partially characterized. For this enzyme, the Lineweaver-Burk's double reciprocal plots of initial rates and D-fructose-6-phosphate (F-6-P) or Mg-ATP concentrations for varying values of cosubstrate concentration gave intersecting lines indicating that Km values for F-6-P (1.05 mM) and ATP (3 μM) were independent of each other. S. cervi PFK, when assayed at inhibitory concentration of ATP (>0.1 mM), exhibited sigmoidal behavior towards binding with F-6-P with a Hill coefficient (n) value equal to 1.8 and 1.7 at 1.0 and 0.33 mM ATP, respectively. D-fructose-1,6-diphosphate (FDP) competitively inhibited the filarial enzyme: Ki and Hill coefficient values being 0.18 μM and 2.0, respectively. Phosphoenolpyruvate (PEP) also inhibited the enzyme competitively with the Ki value equal to 0.8 mM. The Hill coefficient values (>1.5) for F-6-P (at inhibitory concentration of ATP) and FDP suggested its positive cooperative kinetics towards F-6-P and FDP, showing presence of more than one binding sites for these molecules in enzyme protein and allosteric nature of the filarial enzyme. The product inhibition studies gave us the only compatible mechanism of random addition process with a probable orientation of substrates and products on the enzyme surface.

scholarly journals Identification of histidine-122α in human haemoglobin as one of the unknown alkaline Bohr groups by hydrogen-tritium exchange

1978 ◽  
Vol 173 (2) ◽  
pp. 651-657 ◽  
Author(s):  
K Nishikura
Keyword(s):  
Rate Constants ◽  
Imidazole Ring ◽  
Bohr Effect ◽  
Human Haemoglobin ◽  
First Order ◽  
Ph Values ◽  
Pseudo First Order ◽  
Ph Dependent ◽  
Alkaline Bohr Effect ◽  
Total Alkaline

Human carbonmonoxy- and deoxy-haemoglobins were incubated at 37 degrees C in 3H2O at various pH values to measure the pH-dependent hydrogen–tritium exchange at the C-2 position of the imidazole ring of histidine-122alpha. To obtain the pseudo-first-order rate constants for the exchange, k, the two peptides containing histidine-122alpha were isolated and the amounts of tritium incorporated were determined. The rate constants gave pK values for the histidine of 6.1 in carbonmonoxyhaemoglobin and 6.6 in deoxyhaemoglobin, showing that it contributes about 20% to the total alkaline Bohr effect and about 10% at pH7.4.

scholarly journals SARS-CoV-2 Mpro inhibition by zinc ion: structural features and hints for drug design

2021 ◽  
Author(s):  
Deborah Grifagni ◽  
Vito Calderone ◽  
Stefano Giuntini ◽  
Francesca Cantini ◽  
Marco Fragai ◽  
...  
Keyword(s):  
Drug Design ◽  
Binding Site ◽  
Structural Data ◽  
Structural Features ◽  
Zinc Ion ◽  
Zinc Binding ◽  
Main Protease ◽  
Zinc Binding Site ◽  
Organic Inhibitor

Structural data on SARS-CoV-2 main protease in complex with a zinc-containing organic inhibitor gave hints on the presence of a zinc binding site involving the catalytic relevant cysteine and histidine...

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