Abstract
Primary role of peroxidase enzyme is to decompose endogenous hydrogen peroxide, when oxygen radical is being replaced by a less potent radical, which is its cosubstrates oxidized form. During this study, catalytic activity of horseradish peroxidase has been observed in the presence of antioxidants from vitamin group, such as C, E and A, i.e. their water-soluble forms. It was found that vitamin E showed no effect on the enzyme activity and fate of cosubstrate radicals from the group of benzidine derivatives. Vitamin C proceeds enzymatic reaction showing its antioxidative character, and absorbs electrons from radicals, bringing cosubstrate back to its relaxed state. On the other hand, vitamin A plays a role of uncompetitive peroxidase inhibitor, which is visible through decreasing initial rate of catalytic reaction, and is reflected as virtual decrease of enzyme concentration. Furthermore, it prolongs life of endogenous hydrogen peroxide, which could potentially lead to oxidative stress of cells. This inhibitory effect can be used in analytical purpose, for determination of retinol acetate content in a sample.
Highlights
catalytic activity of horseradish peroxidase has been observed in the presence of antioxidants
It was found that vitamin E showed no effect on the enzyme activity and fate
vitamin A plays the role of a noncompetitive peroxidase inhibitor
Summary
Kao i ishrana domaćih životinja i kućnih ljubimaca, sve više uključuje upotrebu raznih mineralno-vitaminskih suplemenata koji zbog načina pripreme često iziskuju oblike rastvorljive u vodi, a to se odnosi i na vitamine rastvorljive u uljima. Tako je iz rena izolovano više od 40 izoenzima peroksidaze o čijim se pojedinačnim aktivnostima nedovoljno zna [3], ali za većinu važi jedan generalni mehanizam katalitičke aktivnosti [4], koji se može predstaviti na način kao što je dato na šemi 1. U određenim uslovima ulogu kosupstrata može preuzeti i sam H2O2, koji tako postaje i akceptor i donor elektrona u isto vreme, ali to za posledicu ima znatno smanjenje, pa čak i potpuni gubitak aktivnosti enzima [9].Tako je utvrđeno da rastuća koncentracija peroksida, mereno na pH 6,3, može brzo da razori čitav molekul peroksidaze, formiranjem nestabilnog kompleksa, nastalog između dva molekula H2O2 i gvožđa u centru hema [10]. Ovo se može manifestovati kao prividno smanjenje ukupne koncentracije enzima u reakcionoj smeši, pa i u ćeliji, što dalje može dovesti do nakupljanja peroksida i doprineti prouzrokovanju oksidativnog stresa [15]
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