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Peroxidases have many potential uses for biotechnological processes. In this review, peroxidase-catalyzed reactions potentially applicable to the petroleum industry are described. Although peroxidases are attractive catalysts for desulfurization, aromatic oxidation and asphaltene transformation, there are important issues that must be overcome before any industrial application can be considered. The opportunities and challenges of enzymatic petroleum biorefining are documented and discussed, with emphasis on the available tools to design a biocatalyst with appropriate performance for the oil and other industries. [ABSTRACT FROM AUTHOR]

Paraoxonasel (PON1), one of HDL-asssociated antioxidant proteins, is known to be sensitive to oxidative stress. Here, the effect of endogenous reducing compounds on Cu2+-mediated inactivation of PON1 was examined. Cu2+-mediated inactivation of PON1 was enhanced remarkably by catecholamines, but not by uric acid or homocysteine. Furthermore, catecholamines such as 3,4-dihydroxyphenylalanine (DOPA), dopamine or norepinephrine were more effective than caffeic acid or pyrocatechol in promoting Cu2+-mediated inactivation of PON1, suggesting the importance of dihydroxybenzene group as well as amino group. DOPA at relatively low concentrations showed a concentration-dependent inactivation of PON1 in a concert with Cu2+, but not Fe2+. The DOPA/Cu2+-induced inactivation of PON1 was prevented by catalase, but not hydroxyl radical scavengers, consistent with Cu2+-catalyzed oxidation. A similar result was also observed when HDL-associated PON1 (HDL-PON1) was exposed to DOPA/Cu2+. Separately, it was found that DOPA at low concentrations (1-6 μM) acted as a pro-oxidant by enhancing Cu2+-induced oxidation of HDL, while it exhibited an antioxidant action at >10 μM. In addition, Cu2+-oxidized HDL lost the antioxidant action against LDL oxidation. Meanwhile, the role of DOPA/Cu2+-oxidized HDL differed according to DOPA concentration; HDL oxidized with Cu2+ in the presence of DOPA (60 or 120 μM) maintained antioxidant activity of native HDL, in contrast to an adverse effect of DOPA at 3 or 6 μM. These data indicate that DOPA at micromolar level may act as a pro-oxidant in Cu2+-induced inactivation of PON1 as well as oxidation of HDL. Also, it is proposed that the oxidative inactivation of HDL-PON1 is independent of HDL oxidation. [ABSTRACT FROM AUTHOR]

Paraoxonase1 (PON1), one of antioxidant proteins to protect low density lipoprotein (LDL) from the oxidation, is known to lose its activity in the oxidative environment. Here, we attempted to elucidate the possible mechanisms for the oxidative inactivation of PON1, and to examine the capability of hydroxyl radicals-inactivated PON1 to prevent against LDL oxidation. Of various oxidative systems, the ascorbate/Cu[sup2+] system was the most potentin inactivating the purified PON1 (PON1) as well as HDLbound PON1 (HDL-PON1). In contrast to a limitedinactivation by Fe[sup2+] (2.0 μM), the inclusion of Cu[sup2+] (0.1-1.0μM) remarkably enhanced the inactivation of PON1 in the presence of ascorbate (0.5 mM). A similar result was also obtained with the inactivation of HDL-PON1. The inactivation of PON1 by ascorbate/Cu[sup2+] was prevented by catalase, but not general hydroxyl radical scavengers, supporting Cu[sup2+]-catalyzed oxidative inactivation.In addition, Cu[sup2+] alone inactivated PON1, either soluble or HDL-bound, by different mechanisms, concentration dependent. Separately, there was a reverse relationship between the inactivation of PON1 and its preventive action against LDL oxidation during Cu[sup2+]-induced oxidation of LDL. Noteworthy, ascorbate/Cu2þ-inactivated PON1, which was charaterized by the partial loss of histidine residues, expressed a lower protection against Cu[sup2+] induced LDL oxidation, compared to native PON1. Based on these results, it is proposed that metal-catalyzed oxidation may be a primary factor to cause the decrease of HDL-associated PON1 activity under oxidative stress, and radicals-induced inactivation of PON1 may lead to the decrease in its antioxidant action against LDL oxidation. [ABSTRACT FROM AUTHOR]