Nitrite-Mediated Inactivation of Human Plasma Paraoxonase-1: Possible Beneficial Effect of Aromatic Amino Acids

Paraoxonase-1 (PON-1) is a high-density-lipoprotein-bound enzyme, and its major function is to prevent oxidation of low-density lipoprotein. Atherogenesis could be related to decreased activity of this enzyme. Nitrites (), either present as a contaminant and/or the main metabolic end product of nitric oxide (NO) degradation, may trigger nitrative damage to PON-1 enzyme. Minimal information is available concerning the effect of nitrite on the enzyme activity and the mechanism which it exerts its effect. The aim of this study was to analyze whether nitrites could play a role in modifying human PON-1 activity. Our results revealed that PON-1 activity was inhibited by nitrite in dose- and time-dependent manner. Site-specific nitration focused on phenolic residues, particularly tyrosine residues of the enzyme, may result in modification of its biological functions. Nitration of phenolic residues occurs via peroxynitrite (ONOO⁻) formation, which requires peroxides and nitrite. Thus, we tested the presence of peroxides, which are found in all plasma samples regardless of nitrite concentration. The inhibition of PON-1 activity by nitrite was significantly reduced by tryptophan, reduced glutathione (GSH), and catalase additions. Therefore, we concluded that nitrites may have a role in the inactivation of PON-1, probably through nitration of enzyme phenyl residues, and additions of individual aromatic amino acids, with highlighting on tryptophan, could be of important value in minimizing the nitrite-induced inhibition of PON-1 enzyme.     

Analysis of a Polynomial System Arising in the Design of an Optical Lattice Filter Useful in Channelization

In this work, we consider design questions for an active optical lattice filter, which is being manufactured at the University of Texas at Dallas, and which has proven to be useful in the signal processing task of RF channelization. The filter can be described by a linear, discrete time state space model. The controlling agents, the gains, are embedded in the matrices intervening in this state space model. Consequently, techniques from linear feedback control theory do not apply. We concentrate on the question of finding real valued gains so that the A matrix of the state space model has a prescribed characteristic polynomial. We find that three of the coefficients can be arbitrarily picked, but that the remaining are constrained by these and the other system parameters. Our techniques use methods from constructive algebraic geometry.     

Synthesis,Characterisation, and in vitro Cytotoxic Activity of Dithiocarbamato Glycoconjugate Half-Sandwich Ruthenium and Osmium Complexes

The synthesis by transmetallation and in-depth characterisation by IR spectroscopy of five half-sandwich ruthenium and osmium dithiocarbamato isonipecotamide glycoconjugate complexes are presented herein. The evaluation of their in vitro cytotoxicity and of the zinc precursors’ in vitro cytotoxicity towards ovarian cancer (A2780 and A2780cisR) and normal prostate (PNT2) cells is reported. While the cytotoxicity of the compounds is rather limited, some selectivity is observed.