Globalization as a worldwide process has significant implications in the area of education. In relation to this trend, the main challenge is to prepare students for the role of competent global citizens. Thus, we tested selected group of students of chemistry in attempt to measure their understanding of global trends in education. Results show positive attitudes towards student mobility, but no vision to develop competence and capacity that will make them quality applicants for international mobility programs. Scarce examples of students engagement in global educational trends only magnifies the need for well researched and organized approach in this area.

Myeloperoxidase (MPO) is a hemoprotein, involved in the leukocyte mediated defense mechanism, and uses hydrogen peroxide (H2O2) and chloride (Cl-) to produce hypochlorous acid. In human saliva and hypochloremic alkalosis syndrome occurring in breast fed infants, the MPO-H2O2 system functions in lower Cl- concentration (10-70 mM) compared to plasma levels (100 mM) as part of the antibacterial defense system. The impact of low Cl- concentration and exposure to high peroxynitrite (ONOO-) synthesized from cigarette smoke or oxidative stress on MPO function is still unexplored. Rapid mixing of ONOO- and MPO caused immediate formation of a transient intermediate MPO Compound II which then decayed to MPO-Fe (III). Double mixing of MPO with ONOO- followed by H2O2 caused immediate formation of Compound II followed by MPO heme depletion, a process that occured independent of ONOO- concentration. Peroxynitrite/H2O2-mediated MPO heme depletion was confirmed by HPLC analysis and in-gel heme staining showing 60-70% less heme content compared to the control. A non-reducing denaturing SDS PAGE showed no fragmentation or degradation of protein. Myeloperoxidase heme loss was completely prevented by pre-incubation of MPO with saturated amounts of Cl-. Chloride binding to the active site of MPO constrains ONOO- binding by filling the space directly above the heme moiety or by causing a protein conformational change that constricts the distal heme pocket, thus preventing ONOO- from binding to MPO heme iron. Peroxynitrite interaction with MPO may serve as a novel mechanism for modulating MPO catalytic activity, influencing the regulation of local inflammatory and infectious events in vivo.

We investigated the potential role of the co-substrate, thiocyanate (SCN–), in modulating the catalytic activity of myeloperoxidase (MPO) and other members of the mammalian peroxidase superfamily (lactoperoxidase (LPO) and eosinophil peroxidase (EPO)). Pre-incubation of SCN– with MPO generates a more complex biological setting, because SCN– serves as either a substrate or inhibitor, causing diverse impacts on the MPO heme iron microenvironment. Consistent with this hypothesis, the relationship between the association rate constant of nitric oxide binding to MPO-Fe(III) as a function of SCN– concentration is bell-shaped, with a trough comparable with normal SCN– plasma levels. Rapid kinetic measurements indicate that MPO, EPO, and LPO Compound I formation occur at rates slower than complex decay, and its formation serves to simultaneously catalyze SCN– via 1e– and 2e– oxidation pathways. For the three enzymes, Compound II formation is a fundamental feature of catalysis and allows the enzymes to operate at a fraction of their possible maximum activities. MPO and EPO Compound II is relatively stable and decays gradually within minutes to ground state upon H2O2 exhaustion. In contrast, LPO Compound II is unstable and decays within seconds to ground state, suggesting that SCN– may serve as a substrate for Compound II. Compound II formation can be partially or completely prevented by increasing SCN– concentration, depending on the experimental conditions. Collectively, these results illustrate for the first time the potential mechanistic differences of these three enzymes. A modified kinetic model, which incorporates our current findings with the mammalian peroxidases classic cycle, is presented.

Heme reduction of ferric lactoperoxidase (LPO) into its ferrous form initially leads to the accumulation of the unstable form of LPO-Fe(II), which spontaneously converts to a more stable species, the two of which can be identified by Soret peaks at 440 and 434 nm, respectively. Our data demonstrate that both LPO-Fe(II) species are capable of binding O2 at a similar rate to generate the ferrous-dioxy complex. Its formation with respect to O2 was first order and monophasic and with rate constants of kon = 3.8 × 104 m–1 s–1 and koff = 11.2 s–1. The dissociation rate constant for the formation of LPO-Fe(II)-O2 is relatively high, in contrast to hemoprotein model compounds. This high dissociation rate can be attributed to a combination of effects that include the positive trans effect of the proximal ligand, the heme pocket environment, and the geometry of the Fe-O2 linkage. Our results have also shown that the decay of the LPO-Fe(II)-O2 complex occurs by two sequential O2-independent steps. The first step involves formation of a short-lived intermediate that can be characterized by its Soret absorption peak at 416 nm and may be attributed to the weakening of the Fe(II)-O2 linkage with a rate constant of 0.5 s–1. The second step is spontaneous conversion of this intermediate to generate the native enzyme and presumably superoxide as end products with a rate constant of 0.03 s–1. A comprehensive kinetic model that links LPO-Fe(II)-O2 complex formation to the LPO catalase-like activity, combined with the classic catalytic cycle, is presented here.