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Biomedical subjects

L G Pedersen

Publications and source records attributed to L G Pedersen.

83 records · Page 5Linked to original sources
PubMed1986

Chemical modification of bovine prothrombin fragment 1 in the presence of Tb3+ ions.

The formaldehyde-morpholine method for the conversion of gamma-carboxyglutamyl (Gla) residues to gamma-methyleneglutamyl (gamma-MGlu) residues has been applied to the modification of bovine prothrombin fragment 1. In the absence of Tb3+ ions or at Tb3+ ion concentrations of 2 Km app and 25 Km app the action of 10,000-fold molar excess of formaldehyde and morpholine, pH 5.0, converts the 10 Gla residues of the protein into 10 gamma-MGlu residues. Modification of the protein using the same conditions but increasing the Tb3+ concentration to 100 Km app provided a homogeneous protein containing 3 gamma-MGlu and 7 Gla residues, bovine 3 gamma-MGlu-fragment 1. The modified protein binds the same number of Ca2+ ions (6-7) as bovine fragment 1. However, the positive cooperatively associated with Ca2+ binding is abolished and the overall affinity for Ca2+ ions is reduced. Fluorescence titrations of 3 gamma-MGlu-fragment 1 using either Ca2+ or Mg2+ ions indicate that the modified protein retains a fluorescence quenching behavior similar to that of the native protein. The modified protein does not bind to phosphatidylserine/phosphatidylcholine vesicles in the presence of Ca2+ ions. Thus the metal ion-induced fluorescence transition exhibited by the bovine protein appears to be a necessary but not sufficient condition for phospholipid binding.

Amino Acids↗
PubMed1986

The effect of divalent metal ions on the electrophoretic mobility of bovine prothrombin and bovine prothrombin fragment 1.

Examination of metal ion-dependent effects on the electrophoretic mobility of bovine prothrombin and fragment 1 provides a useful and sensitive method for investigation of conformational processes in these proteins. Utilization of this method reveals a conformational change in bovine prothrombin and fragment 1 which occurs at low metal ion concentrations. Equilibrium dialysis studies indicate that the metal ion-induced shape change occurs concomitant with binding of a single calcium ion/molecule of prothrombin or fragment 1. Mixed metal electrophoretic mobility studies with Mg2+ and Ca2+ have demonstrated the "synergistic" effect for fragment 1 observed by others. Mixed metal equilibrium dialysis has provided experimental support for this observation and allows us to conclude that two tight Ca2+ sites are not affected by low Mg2+ concentrations and that the third Ca2+ site is also a tight site for Mg2+. Thus, at low Mg2+ concentrations and upon the addition of Ca2+, there are effectively three tight sites; consequently more Ca2+ will bind to the protein at lower total Ca2+ ion concentrations.

Animals↗
PubMed1986

A theoretical study of the binding of polychlorinated biphenyls (PCBs), dibenzodioxins, and dibenzofuran to human plasma prealbumin.

Binding energies to human plasma prealbumin using the energy minimization program AMBER are found for a series of polychlorinated biphenyls, dibenzodioxins, and dibenzofuran. Corrections for solvation free energies of the chlorinated analogues lead to estimates of the differential free energies of complex formation. These are compared in a number of cases to known experimental log (KPCB/Kref) values. The theory correctly separates strong, intermediate, and nonbinders. On the basis of calculations, 2,3,7,8-tetrachlorodibenzodioxin and 2,3,7,8-tetrachlorodibenzofuran are predicted to be strong binders, 3,3',5,5'-tetrachlorodiphenoquinone is predicted to be a weak binder, and octachlorodibenzodioxin is predicted to not bind at all. This theoretical model for prealbumin interactions may be of use in estimating the toxic potential of PCBs and related halogenated aromatic hydrocarbons of environmental importance.

Benzofurans↗
PubMed1986

Synthesis of a gamma-carboxyglutamic acid containing heptapeptide corresponding to bovine prothrombin residues 17-23.

The vitamin K-dependent proteins involved in blood coagulation processes each contain a small cystine loop with the sequence -Gla-Cys-X-Gla-Gla-X-Cys-. A method for the synthesis of the heptapeptide derivative representing the 17-23 sequence of bovine prothrombin, Z-Gla-Cys-Leu-Gla-Gla-Pro-Cys-OBzl, has been developed. The 25Mg2+ n.m.r. spectrum of the heptapeptide derivative has been obtained and is compared to the n.m.r. spectra obtained from the interaction of 25Mg2+ with Z-Gla-OMe and Z-Gla-Gla-OMe.

1-Carboxyglutamic Acid↗
PubMed1986

An Ab initio study of the relationship between nitroarene mutagenicity and electron affinity.

Electron affinities, approximated by lowest unoccupied molecular orbital (LUMO) energies, were determined for an extensive group of nitrated polycyclic aromatic hydrocarbons by ab initio methods at the STO-3G level. Significant correlations were demonstrated between nitroarene LUMO energy and the corresponding mutagenic activity in Salmonella typhimurium strains TA98, TA100, TA1537, and TA1538. An analogous correlation using Hückel calculations was substantially poorer. A correlation between nitro group rotation and LUMO energy was related to pi-conjugation about the C--N bond. Analysis of aryl substituent effects on nitrenium ion stability implicated additional nitro substitution in certain systems to be destabilizing. The results suggest a means for predicting nitroarene mutagenic activity and for assessing the role of metabolic intermediates.

Chemical Phenomena↗
PubMed1986

Conformation of the 18-23 loop region of bovine prothrombin in the absence and presence of a model Ca2+ ion. An energy minimization study.

The conformation of the cyclic peptide Ac-Cys-Leu-Gla-Gla-Pro-Cys-NHMe, representing the 18-23 disulfide loop of bovine prothrombin, was studied by energy minimization with the ECEPP (Empirical Conformational Energy Program for Peptides) algorithm. Parameters for charge and geometry for the gamma-carboxyglutamic acid (Gla) residue were obtained for inclusion in the ECEPP data set. Construction of the 18-23 cyclic peptide, for which no crystal structure is available, was carried out by using a scheme that took advantage of the constraints imposed by the requirement of disulfide ring closure and utilized known low-energy structures of single residues and dipeptides. Both cis and trans isomers about the Gla 21-Pro 22 peptide bond were considered. The lowest-energy conformation found for the isolated 18-23 cyclic peptide with arbitrary reduction of the charge on the Gla residues (to simulate hydration roughly) is a trans form, differing in energy by 11 kcal-mol-1 from the lowest-energy cis form. However, when the energy calculation includes one model Ca2+ ion, X2+, introduced at a fixed distance of 2.3 A from a single oxygen atom of either of the side-chain carboxyl groups of Gla with the C delta-O-X2+ bond angle fixed at one of three values, the lowest-energy cis conformation is about 1 kcal-mol-1 lower in energy than the lowest-energy trans conformation; i.e. the two structures have similar energies. In these structures, four oxygen atoms, two from each Gla side-chain, approach the model Ca2+ ion closely, in a manner similar to that seen in crystals of calcium alpha-ethylmalonate (Zell, A., Einspahr, H. & Bugg, C.E. (1985) Biochemistry 24, 533-537). It appears that the binding of Ca2+ to the 18-23 cyclic peptide may alter the equilibrium between cis and trans structures such that the fraction of cis isomers is greater in the presence of Ca2+.

Animals↗
PubMed1985

A kinetic model describing the interaction of bovine prothrombin fragment 1 with calcium ions.

A kinetic model is derived for the interaction of bovine prothrombin fragment 1 with calcium ions. The model requires binding of a minimum of two calcium ions for induction of the observed biphasic fluorescence decrease as a function of time. The model is shown to be consistent with experimental kinetic and equilibrium data by fitting theoretical curves for the biphasic fluorescence change to the data through exact solution of the nonlinear differential rate equations derived from the model. The rate constants for the binding of these two required calcium ions are calculated from the solutions as best fit parameters. The thermodynamic equilibrium constants, K1 and K2, for the binding of these two calcium ions are calculated from ratios of the forward and reverse rate constants as 0.6 X 10(4) and 5.4 X 10(4), respectively. Thus, the model correctly predicts positively cooperative calcium ion binding for at least the two calcium ions required to induce fluorescence quenching.

Animals↗