Effects Of Divalent Metal Cations Research Articles

The effect of divalent metal cations on the inhibition of human coagulation factor Xa by plasma proteinase inhibitors

The inactivation of human coagulation factor Xa by the plasma proteinase inhibitors α 1-antitrypsin, antithrombin III and α 2-macroglobulin in purified systems was found to be accelerated by the divalent cations Ca 2+, Mn 2+ and Mg 2+. The rate constant for the inhibition of factor Xa by antithrombin III rose from 2.62·10 4 M −1-·min −1 in the absence of divalent cations to a maximum of 6.40·10 4 M −1·min −1 at 5 mM Ca 2+, 8.10·10 4 M −1·min −1 at 5 mM Mn 2+, with a slight decresae in rate at higher cation concentrations. Mg 2+ caused a gradual rise in rate constant to 5.65·10 4 M −1·min −1 at 20 mM. The rate constant for the inhibition of factor Xa by α 1-antitrypsin in the absence of divalent cations was 5.80·10 3 M −1·min −1. Ca 2+ increased the rate to 1.50·10 4 M −1·min −1 at 5 mM and Mn 2+ to 2.40·10 4 M −1·min −1 at 6 mM. The rate constant for these cations again decreased at higher concentrations. Mg 2+ caused a gradual rise in rate constant to 1.08·10 4 M −1·min −1 at 10 mM. The rate constant for the factor Xa- α 2-macroglobulin reaction was raised from 6.70·10 3 M −1·min −1 in the absence of divalent cations to a maximum of 4.15·10 4 M −1·min −1 at 4 mM Ca 2+, with a decreae to 3.05·10 4 M −1 at 10 mM. These increases in reaction rate were correlated to the binding of divalent cations to factor Xa by studying changes in the intrinsic fluorescence and dimerization of factor Xa. The changes in fluorescence suggested a conformational change in factor Xa which may be responsible for the increased rate of reaction, whilst the decrease in rate constant at higher concentrations of Ca 2+ and Mn 2+ may be due to factor Xa dimerization.

Effects of Divalent Metal Cations on Circular Dichroism and 1H Nuclear Magnetic Resonance Spectra of Linear and Cyclic Peptides Having Side-chain Imidazolyl and Acetamido Groups

Abstract A linear peptide, N-t-butoxycarbonyl-S-acetamidomethyl-l-cysteinyl-d-leucyl-l-histidyl-S-acetamidomethyl-l-cysteinyl-d-leucyl-l-histidine methyl ester (1) was synthesized by the solid phase method. Subsequent cyclization by the azide method offered a cyclic peptide, cyclo-S-acetamidomethyl-l-cysteinyl-d-leucyl-l-histidyl-S-acetamidomethyl-l-cysteinyl-d-leucyl-l-histidyl (2). The circular dichroism (CD) and 1H NMR were observed for these peptides 1 and 2, in the absence and presence of metal cations, Zn(II), Ca(II), Mg(II). Spectral results for Zn(II) complexes indicated striking contrasts to those of Ca(II) and Mg(II) complexes. Thus, in H2O, the addition of Zn(II) caused CD spectral changes for both peptides, while Ca(II) and Mg(II) did not cause changes in any CD spectral region. In methanol, the additions of Zn(II) and Ca(II) caused CD changes, while the addition of Mg(II) did not cause any CD changes. The changes caused by adding Zn(II) were quite different from those by Ca(II), suggesting that Zn(II) is coordinated with the peptides in a mode different from that of Ca(II). 1H NMR data also suggested the different coordination mode between these two metal complexes in methanol.

Effects of divalent metal cations in the growth medium upon sensitivity of batch-grown Pseudomonas aeruginosa to EDTA or polymyxin B.

The sensitivity of batch grown Pseudomonas aeruginosa to ethylenediaminetetraacetic acid (EDTA), ethyleneglycol‐bis(2‐aminoethyl ether)‐N, N‐tetraacetic acid (EGTA) and to polymyxin depended upon the nature and concentration of divalent metal cations (Ca2+, Mg2+, Ba2+, Mn2+, Sr2+, Zn2+, Fe2+, Al3+) present in the simple salts‐glucose growth medium. Sensitivity to the antibacterial agents was measured in terms of per cent decrease in optical density which was proportional to total count. The rate of decrease in optical density and the per cent decrease after a given time were proportional to the cation content of the growth medium. The lytic action of the agents correlated to some extent with the stability constants of the cation for the two chelating agents.The data support the theory that EDTA and polymyxin both act initially at a common site of action, namely the Mg2+ and Ca2+ cross bridges that stabilize components of the outer membrane.

Effect of metal cations on misincorporation by E. coli DNA polymerases

The effects of divalent metal cations on DNA polymerase activity of E. coli polymerase I, II or III and on their fidelities during DNA synthesis in vitro have been examined. Carcinogenic or mutagenic metal at the concentration which decreases polymerase activity increased misincorporation, whereas noncarcinogenic metal did not change the fidelity even at a concentration inhibiting polymerase. The change in 3′ → 5′ exonuclease activity of polymerase by metal ions was not responsible for the increase in the misincorporation. The influences of metals on Km for the substrate and template-primer were also observed.

Role of divalent metal cations in heavy meromyosin-adenosine triphosphate complex.

Effects of divalent metal cations on the heavy meromyosin ATPase [EC 3.6.1.3] reaction were studied by measuring the ATP-induced ultraviolet absorption difference spectrum at the pre-steady and steady states, and the Pi-liberation at the steady state. Effects of MgCl2 concentration on apparent values of the parameters, the maximum velocity and Michaelis constant of the ATPase, the velocity of formation of the difference spectrum, and the molar difference absorption coefficient were investigated. From the analysis of the results, the role of divalent cation on the ATPase reaction has been elucidated according to a reaction mechanism which involves two Michaelis complexes, ES and EMS, where M represents the divalent metal cation. Rate constant of the step from EMS to give product, k2′, and the dissociation constant of EMS to EM and S, K2′, were determined. In the presence of any one of Mg2+, Co2+, Mn2+ or Ca2+, logk2′ vs. logK2′ plot was linear. The plot of logk2′ vs. reciprocal of ionic radius of the cation was also linear. Results indicate that the smaller the ionic radius of cation, the more strongly ATP is bound by EM and the more slowly product is formed from EMS. The pH dependency of an apparent dissociation constant of EMS to ES and M yielded a second order dissociation curve of pKa=7.3. Two imidazole groups are suggested to participate in the binding of the divalent cation.