Role Of Manganese Ions Research Articles

Electron spin resonance investigation of impurity and intrinsic defects in Nb-doped BaTiO3 single crystal and ceramics

Electron spin resonance (ESR) spectra of impurity and intrinsic defects have been measured at 4.2–295 K in Nb-doped BaTiO3 single crystals and ceramics to clarify their role in the conductivity and positive temperature coefficient of resistivity (PTCR effect). The measurements revealed a small amount of Fe3+, Cr3+, and Mn2+ impurities, which change their valence state (for example, Cr5+→Cr3+, Mn4+→Mn2+) with increased Nb concentration due to the compensation of the excess charge of Nb5+ ions. Besides the 3d-metal impurities, several types of Ti3+ polaronic and possible fluctuon states, where electrons can be localized near ferroelectric domain boundaries, have been revealed as well. All of them are associated with Ti3+ lattice ions and not with Nb5+∕4+ impurity, which apparently represents rather a very shallow donor level. The data obtained strongly support the polaronic origin of Nb-doped BaTiO3 conductivity at T<300K. Comparative investigations of ESR spectra in single crystals and ceramics of the same kind of BaTiO3 together with computer simulation allowed us unambiguously to ascribe complex ESR signals observed in ceramic samples to Cr3+, Mn2+, and Fe3+ ions and Ti3+ polarons and/or fluctuons. The role of manganese ions at grain boundaries in the PTCR effect is discussed as well.

Role of manganese ions on the stability of ZnF2–P2O5–TeO2 glass system by the study of dielectric dispersion and some other physical properties

ZnF2–P2O5–TeO2 glasses containing different concentrations of MnO (ranging from 0 to 0.6%) were prepared. A number of studies, viz. differential thermal analysis, optical absorption, thermo luminescence, infrared spectra, magnetic susceptibility, elastic properties (Young's modulus Y, shear modulus n and micro hardness H) and dielectric properties (constant ε, loss tanδ, a.c. conductivity σac over a range of frequency and temperature and dielectric breakdown strength), of these glasses were carried out as a function of manganese ion concentration. The analysis of the results indicate manganese ions mostly exist in Mn2+ state in these glasses when the concentration of MnO≤0.4% and above this concentration manganese ions predominantly exist in Mn3+ state; from this analysis an attempt is made to identify the role of these ions on the stability of glass network.

In vivo stimulation-induced release of manganese in rat amygdala

The role of manganese ions in neural functions is poorly understood because of the low level of manganese in the brain. An excess of this ion is associated with neurological disorders such as extrapyramidal symptoms. We demonstrated that manganese may be taken up by piriform neurons (tertiary olfactory neurons) after release from the terminals of secondary olfactory neurons, in which 54 Mn taken up by the soma may be anterogradely transported [A. Takeda, Y. Kodama, S. Ishiwatari, S. Okada, Manganese transport in the neural circuit of Rat CNS, Brain Res. Bull. (45) (1998) 149–152]. Here we demonstrate for the first time that 54 Mn previously taken up into the amygdala is released with neurotransmitters into the extracellular space during stimulation with high K +. The results suggest that the role of manganese ions in the amygdala, and probably in the olfactory system, is dynamically linked to neural signalling processes.

Localization and Functional Analysis of the Substrate Specificity/Catalytic Domains of Human M-form and P-form Phenol Sulfotransferases

Human monoamine (M)-form and simple phenol (P)-form phenol sulfotransferases (PSTs), which are greater than 93% identical in their primary sequences, were used as models for investigating the structural determinants responsible for their distinct substrate specificity and other enzymatic properties. A series of chimeric PSTs were constructed by reciprocal exchanges of DNA segments between cDNAs encoding M-form and P-form PSTs. Functional characterization of the recombinant wild-type M-form, P-form, and chimeric PSTs expressed in Escherichia coli and purified to homogeneity revealed that internal domain-spanning amino acid residues 84-148 contain the structural determinants for the substrate specificity of either M-form or P-form PST. Data on the kinetic constants (Km, Vmax, and Vmax/Km) further showed the differential roles of the two highly variable regions (Region I spanning amino acid residues 84-89 and Region II spanning amino acid residues 143-148) in substrate binding, catalysis, and sensitivity to the inhibition by 2,6-dichloro-4-nitrophenol. In contrast to the differential sulfotransferase activities of M-form and P-form PSTs toward dopamine and p-nitrophenol, the Dopa/tyrosine sulfotransferase activities were found to be restricted to M-form, but not P-form, PST. Furthermore, the variable Region II of M-form PST appeared to play a predominant role in determining the Dopa/tyrosine sulfotransferase activities of chimeric PSTs. Kinetic studies indicated the role of manganese ions in dramatically enhancing the binding of D-p-tyrosine to wild-type M-form PST. Taken together, these results pinpoint unequivocally the sequence encompassing amino acid residues 84-148 to be the substrate specificity/catalytic domain of both M-form and P-form PSTs and indicate the importance of the variable Regions I and II in determining their distinct enzymatic properties.

Bovine Galactosyl Transferase. Substrate . Manganese Complexes and the Role of Manganese Ions in the Mechanism

The role of Mn2+ in the reaction catalysed by the galactosyl transferase of bovine milk and colostrum was studied by steady-state kinetic methods at pH 7.4 and 37°C. The association constants for the binding of Mn2+ by UDP-galactose and by the buffer species used (3-[N-morpho-lino]propanesulphonate) were measured by electron spin resonance spectroscopy and the concentrations of all the species present in the substrate mixture of Mn2+· UDP-galactose and N-acetyl-glucosamine were calculated. Previous evidence indicated that high Mn2+ concentrations activate the reaction beyond what is expected from the Michaelis-Menten equation. At such levels (up to 40 mM), the concentration of free Mn2+ was found to be proportional to total Mn within 3%. Experimental data produced as a function of total Mn concentration and total UDP-galactose (i.e. free UDP-galactose plus MnUDP-galactose) concentration could be interpreted in terms of rate equations written in relatively simple form with free Mn2+ and total UDP-galactose concentrations as variables, corresponding to a large variety of kinetic models involving Mn2+, UDP-galactose and MnUDP-galactose as substrates. A group of related mechanisms could not be eliminated at this stage and experiments were carried out in which the concentrations of two of the substrates were varied at either a constant ratio or a constant product depending on how they were involved in the Mn2+: UDP-galactose association reaction. A choice between the two final mechanisms was made by applying statistical non-linear least-squares methods. The most likely mechanism was one in which, after the addition of Mn2+ to the enzyme, the substrates UDP-galactose and MnUDP-galactose added as alternatives to produce two branches, in each of which was added N-acetylglucosamine followed by the release of N-acetyllactosamine, then the Mn2+ complex of UDP, and finally (in the branch in which MnUDP-galactose had been the substrate) free Mn2+.

Galactosyl transferase: The role of manganese ions in the mechanism

Double reciprocal plots for galactosyl transferase with UDP-galactose varying at several fixed Mn 2+ concentrations are a series of straight lines. Different laboratories disagree as to whether the intercepts on the 1 v axis are independent of Mn 2+ or not. PbCl 2 added in a fixed proportion is shown theoretically to be incapable of introducing such a dependence on total metal ion concentration. A mechanism derived from extensive kinetic studies is presented, with alternative pathways for free UDP-galactose and the Mn 2+ complex as substrates, following obligatory Mn 2+ addition, and the conflicting results from different laboratories are explained on the basis of a different flux through the alternative pathways under different conditions.

Role of Manganese Ions on the Modification of the Mutagenic Activity of Some Alkylating Agents

The mutagenic activity of manganese ions when applied either alone or in various combination with two alkylating mutagens, ethyleneimin and propane Sultone were studied using dormant seeds of pea as a test material. The criteria for measuring the biological damage were seed lethality, seedling injury, mitotic and meiotic chromosomal aberrations and the frequency of leaf spots on first two leaves of the seedling. Mn++ by itself does not cause much seed or seedling injury but produces a moderate amount of chromosomal aberrations with a corresponding increase in the frequency of leaf spotting. When El treatment were accompanied by Mn++ there was an overall reduction in the biological damage caused by El alone, where as when Mn++ was given prior to PS treatment, there was an overall increase in the damage caused by PS alone. A positive correlation was found between chromosomal aberrations and the frequency of leaf spotting.Data have been discussed with special reference to the probable mode of action of manganese ions and its influence on the activity of other mutagens.