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Biomedical subjects

B Sarkar

Publications and source records attributed to B Sarkar.

At least 73 records · Page 4Linked to original sources
PubMed1991

Metal binding to heparin monosaccharides: D-glucosamine-6-sulphate, D-glucuronic acid, and L-iduronic acid.

In order to ascertain which residues in heparin may be responsible for its metal binding capacities we have investigated metal binding to some of its component monosaccharides by 1H and 13C NMR. The diamagnetic Zn ion and the paramagnetic Ni ion were used as probes. 4-Methylumbelliferyl-2-deoxy-2-acetamido-6-O-sulpho-D-glucosamine was used as a model for O-sulphates. Only weak interactions with the sulphate group were found. The 4C1 ring conformation of sodium methyl-beta-D-glucopyranosiduronate was not perturbed by binding to its carboxylate and little evidence exists for chelation. By contrast, the ring conformation of the sodium methyl-alpha-L-idopyranosiduronate is affected by the addition of Zn greater than Pb greater than Cd greater than Ca much greater than K ions. The sodium salt is suggested to be an equilibrium mixture of the 2SO and 1C4 ring conformations. Cation binding to the carboxylate group shifts this equilibrium towards the 1C4 conformation and suggests additional binding to O5 or, less likely, O4. This effect appears to be electrostatic in nature, as excess Na and protonation produce similar shifts. Lead complexation is different from the other ions and suggests some covalent character. The control of the ring conformation of iduronic acid by metal ions may have biological implications for the action of heparin and heparin-like compounds.

Cadmium↗
PubMed1991

The influence of zinc-binding ligands in fetal circulation on zinc clearance across the in situ perfused guinea pig placenta.

Although zinc is essential for normal fetal growth and development, little is known about factors that influence its transfer across the placenta. The in situ perfused guinea pig placenta model was used to study the influence of zinc-binding ligands in fetal circulation on maternofetal placental zinc transfer. A placenta of each anesthetized sow was perfused (on the fetal side) with a physiological perfusate via the umbilical vessels, with the fetus excluded. The sow was infused intravenously with 65Zn as a tracer of placental zinc clearance and with antipyrine as an indirect indicator of maternal placental blood flow. Maternal plasma and placental effluent samples collected at intervals were counted for 65Zn with a gamma counter, and the absorbance of nitrosated antipyrine was measured at 350 nm. The addition of physiological levels of zinc-binding ligands (albumin, L-histidine and L-cysteine) to the perfusate increased the relative maternofetal clearance of zinc across the placenta calculated as zinc clearance/antipyrine clearance [mean +/- SEM; 0.113 +/- 0.016 vs. 0.062 +/- 0.012; ligands vs. no ligands; n = 8; P less than 0.05]. The results suggest that the availability of zinc-binding ligands in fetal circulation is one determinant factor of placental zinc transfer.

Animals↗
PubMed1991

Binding of cadmium(II) and zinc(II) to human and dog serum albumins. An equilibrium dialysis and 113Cd-NMR study.

The binding of Cd(II) and Zn(II) to human serum albumin (HSA) and dog serum albumin (DSA) has been studied by equilibrium dialysis and 113Cd(II)-NMR techniques at physiological pH. Scatchard analysis of the equilibrium dialysis data indicate the presence of at least two classes of binding sites for Cd(II) and Zn(II). On analysis of the high-affinity class of sites, HSA is shown to bind 2.08 +/- 0.09 (log K = 5.3 +/- 0.6) and 1.07 +/- 0.12 (log K = 6.4 +/- 0.8) moles of Cd(II) and Zn(II) per mole of protein, respectively. DSA bound 2.02 +/- 0.19 (log K = 5.1 +/- 0.8), and 1.06 +/- 0.15 (log K = 6.0 +/- 0.2) moles of Cd(II) and Zn(II) per mole of protein, respectively. Competition studies indicate the presence of one high-affinity Cd(II) site on both HSA and DSA that is not affected by Zn(II) or Cu(II), and one high-affinity Zn(II) site on both HSA and DSA that is not affected by Cd(II) or Cu(II). 113Cadmium-HSA spectra display three resonances corresponding to three different sites of complexation. In site I, Cd(II) is most probably coordinated to two or three histidyl residues, site II to one histidyl residue and three oxygen ligands (carboxylate), while for the most upfield site III, four oxygens are likely to be involved in the binding of the metal ion. The 113Cd(II)-DSA spectra display only two resonances corresponding to two different sites of complexation. The environment around Cd(II) at sites I and II on DSA is similar to sites I and II, respectively, on HSA. No additional resonances are observed in any of these experiments and in particular in the low field region where sulfur coordination occurs. Overall, our results are consistent with the proposal that the physiologically important high-affinity Zn(II) and Cd(II) binding sites of albumins are located not at the Cu(II)-specific NH2-terminal site, but at internal sites, involving mostly nitrogen and oxygen ligands and no sulphur ligand.

Animals↗
PubMed1991

Outcome of teenage pregnancy and labour: a retrospective study.

During the period of study of 3 years (1985-1987), 4698 (18.68%) cases of labour in teenage mothers were recorded out of a total of 25,142 deliveries in the obstetric unit. Preponderance of primigravida (76.6%) and cases from rural areas (51.3%) were recorded. Antenatal care was nil or inadequate in 48.6% cases. Eclampsia and pre-eclampsia affected teenage mothers (10.6%) were much more frequent than mothers of 20 years of age and above (5.2%). Incidence of 30% low birth weight baby, 20.1% prematurity and 16.4% perinatal mortality were recorded.

Adolescent↗
PubMed1990

Interactions of a molybdenum(VI) oxo-cation with some uronic acids: a 1H- and 13C-nuclear magnetic resonance study.

The interactions of molybdate, [MoO4]2- with some uronic acids in aqueous D2O solution were studied by 1H- and 13C-NMR. Evidence is presented for a specific binding site of an Mo(VI) oxo-cation (Mo2O5(2+] with alpha-,beta-D-glucuronic acid. It is proposed that complexation involves the carboxylate oxygen (O-6b) and O-4 of the hydroxyl oxygen in a pyranose form (4C1), in the pH region 3.5-5.8.

Carbon Isotopes↗
PubMed1990

The effect of zinc levels in fetal circulation on zinc clearance across the in situ perfused guinea pig placenta.

Although zinc is essential for normal fetal growth and development, little is known about factors that influence its transfer across the placenta. The in situ perfused guinea pig placenta model was used to study the influence of the zinc concentration of fetal circulation on maternofetal placental zinc transfer. A placenta of the anaesthetized sow was perfused (on the fetal side) with a physiological perfusate via the umbilical vessels, with the fetus excluded. The sow was infused intravenously with 65zinc as a tracer of placental Zn clearance, and with antipyrine as an indirect indicator of maternal placental blood flow. Maternal plasma and placental effluent samples collected at intervals were counted for 65zinc by gamma counter, and the absorbance of nitrosated antipyrine was measured at 350 nm. Varying the mean zinc concentration in the perfusate from 0.176 to 1.87 mg/L had no effect on relative zinc clearance calculated as zinc clearance/antipyrine clearance (mean +/- SEM; 0.085 +/- 0.010 vs. 0.114 +/- 0.018; n = 6; p greater than 0.05). The results suggest that short-term changes in fetal zinc status do not influence placental zinc transfer.

Animals↗
PubMed1990

Nickel binding by isolated human trophoblast cells.

Isolated human trophoblast cells were used for the first time to mimic the placental metabolism of nickel. The retention of nickel by the trophoblast cells was assessed in presence of different nickel ligands. Nickel chloride and nickel-albumin showed an initial rapid binding to human trophoblast cells reaching a quasi-steady state after 30 min. Albumin, however, reduced the binding of nickel to the cells. Nickel-histidine showed slow initial binding, although no saturation was achieved. The results for nickel-histidine complexes are similar to those observed in in vivo experiments.

Absorption↗
PubMed1989

Synthesis and copper(II)-binding properties of the N-terminal peptide of human alpha-fetoprotein.

The N-terminal native sequence tripeptide of alpha-fetoprotein, L-threonyl-L-leucyl-L-histidine N-methylamide, was synthesized and its interaction with Cu(II) ions was investigated by potentiometric titration at 25 degrees C in 0.15 M-NaCl and by visible-absorption, e.p.r. and n.m.r. spectroscopy. Analyses of the results in the pH range 4-10 indicated the presence of multiple complex species in solution: MHL, MH-2L, MHL2, ML2 and MH-1L2, where M, H and L represent metal ion, proton and ligand anion respectively. Only the species MH-2L and MH-1L2 are present in significant amounts at physiological pH. The results of the visible-absorption spectroscopy are consistent with the findings of species distribution that MH-2L is the major complex species detected above physiological pH that has the spectral characteristics of lambda max. = 523 nm and epsilon max. = 98 M-1.cm-1. The nine superhyperfine lines in e.p.r. spectra of the major species MH-2L strongly support the co-ordination of four nitrogen atoms by Cu(II). Both 1H- and 13C-n.m.r. studies suggest that the species MH-2L is a square-planar complex. The results from the equilibrium-dialysis experiments showed that this peptide is able to compete with albumin for Cu(II) ions. At equimolar concentrations of albumin and the peptide, about 52% of the Cu(II) was bound to the peptide. The possibility that alpha-fetoprotein plays an important role as the Cu(II)-transport protein in fetal life is discussed.

Copper↗
PubMed1988

The metabolism of metals in rat placenta.

The status and transfer of metals across the rat placenta were studied by subcellular and molecular fractionations of this organ at 2 and 24 h after iv injection of radiolabeled metals. The soluble and nuclear fractions showed higher contents of copper and zinc, whereas most of the nickel was associated with the soluble fraction. Cadmium was almost evenly distributed between the microsomal and nuclear fractions. Gel filtration of the soluble fractions showed nickel associated with an unknown low molecular weight form; zinc with high molecular weight proteins; copper with metallothionein, ceruloplasmin, and high molecular weight proteins; and cadmium with high molecular weight proteins and metallothionein.

Animals↗
PubMed1987

Isolation and two-dimensional 1H-NMR of peptide [1-24] of dog serum albumin and studies of its complexation with copper and nickel by NMR and CD spectroscopy.

The NH2-terminal peptide fragment [1-24] of dog serum albumin was obtained by controlled peptic digestion of the protein. The peptide was purified to homogeneity by gel filtration and ion-exchange chromatography. The NMR assignments of the protons of the individual amino acid residues were made by using two-dimensional correlation matrix, spin-decoupling experiments and analysis of the titration curves. The polypeptide itself has a random-coil conformation. There is a conformational change as a function of pH, but it does not arise from any direct involvement of the amino acid side chains. Complexation of the peptide fragment with Ni(II) and Cu(II) has been investigated by NMR and CD. The Ni(II) complex is in slow exchange with the free ligand on the NMR time scale. The complexation involves the alpha-NH2, three deprotonated amide nitrogens of Ala-2, Tyr-3 and Lys-4 residues. The phenolate oxygen of Tyr-3 is not involved in the metal binding; however, an interaction between the aromatic ring and the metal ion is likely. The CD results of Cu(II)-binding to this peptide suggest that the complexation takes place from the terminal NH2 and step by step to three deprotonated amide nitrogens. There is no major conformational change of the peptide fragment upon complexation.

Animals↗
PubMed1987

Metal protein interactions.

Proteins associated with metals serve many important biological functions. The amino acid residues provide the functional groups in a protein which are the potential ligands for a metallic cation. Metals impart various effects on protein structure and bring about overall structural stability. These effects are seen in quarternary, secondary and tertiary structures of the protein. There are varieties of approaches to study metal protein interactions. The earliest technique being the equilibrium dialysis which is still used extensibly to determine the binding strength and the number of metals bound per protein molecule. There are a number of other techniques available which provide precise information about the nature of metal binding sites. They include electron spin resonance, UV and visible spectoscopy, nuclear magnetic resonance, resonance Raman, X-ray crystallography, X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (XAFS), etc. Selected metal protein interactions are discussed in this review. Albumin is the major plasma protein in blood which transports a number of metals. Detailed studies of Cu(II) and Ni(II) binding to albumin suggests that both metals have the same specific binding site at the NH2-terminal tripeptide sequence (Asp1-Ala2-His3...) involving the Asp alpha-NH2, His3 N (1) imidazole, two deprotonated peptide nitrogens (Ala2NH and His3NH), and Asp1 COO- group. Transferrin transports Fe(III) in blood. The protein possesses two metal-binding sites, each within a domain of bilobal proteins. Presence of carbonate is an important feature of Fe(III)-binding to transferrin. The binding site has been postulated as one involving Tyr 185 and Tyr 188 and suggests that two of the three histidines His 119, His 207 and His 249 also serve as ligands. Arginine 145 is a likely anchor for the carbonate anion. Superoxide dismutase is an enzyme found in erythrocytes which catalyzes the dismutation of superoxide radical. The protein is a dimer made up of two equivalent subunits. The subunits are held together by noncovalent interactions. For optimal enzymatic activity, at least two of the protein's four metal ions must be cupric. The results of the X-ray crystal structural analysis for Cu(II) and Zn(II) containing protein have been reported. In the metal-binding region of one subunit, Cu(II) and Zn(II) are separated by approximately 6A. The Cu(II) is bound to imidazole side chains of histidines 44, 46, 61 and 118 in a distorted square planar arrangement. The imidazole ring of histidine 61 is believed to be deprotonated and to serve as a bridge between Cu(II) and Zn(II).(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1986

Nickel binding to the C-terminal tryptic fragment of a peptide from human kidney.

In kidney the nickel ion exists primarily as soluble cytoplasmic complexes. We have recently identified a major component of these complexes in the human kidney as a Ni(II) complex of a low molecular weight anionic peptide (Templeton, D.M. and Sarkar, B. (1985) Biochem. J. 230, 35-42). We have now purified a small amount of this peptide to homogeneity and developed an HPLC technique to study its metal-binding properties on sub-nanomole quantities. We are able to demonstrate a binding stoichiometry of one Ni atom per molecule of peptide, with an apparent dissociation constant of 1.1 X 10(-5) M. A similar site exists for Cd. The site for Ni persists after trypsinization, and is localized in the 20-residue C-terminal tryptic fragment of the peptide.

Amino Acids↗