Non-Competitive Inhibition of Xanthine Oxidase by N-Nitrosomorpholine: An In Vitro Study

Nitrosamines can be formed from nitrate. Nitrate is not actually toxic to mammals but can be reduced to nitrite. Nitrite, on the other hand, reacts with amino groups to form the carcinogenic N-nitroso compound. N-nitrosomorpholine (NMOR) is a carcinogenic compound that is included in the nitrosamine class and is the most common type of nitrosamines. Xanthine oxidase (XO) is an enzyme that catalyzes the hydroxylation of hypoxanthine to xanthine and xanthine to uric acid in purine metabolism. Excessive production and/or inadequate excretion of uric acid causes hyperuricemia. This condition is associated with kidney and cardiovascular diseases, especially gout. In order to prevent hyperuricemia and therefore gout, suppressing the activity of the XO enzyme is one of the main targets. In our study, the possible inhibitory effects of NMOR on the activity of the XO enzyme were investigated by spectrophotometric method. XO activity was evaluated in the presence of different concentrations of NMOR and analyzed using Lineweaver-Burk plot. The Km value was determined as 0.55 mM and the Vmax value was determined as 2.45 U/ml. Finally, it was determined that the XO enzyme was inhibited non-competitively by NMOR. Inhibition of XO enzyme with the help of NMOR may lead to functional deficiencies by disrupting the pathway in which purines are metabolized, as well as mediating the control of the production of uric acid formed in purine metabolism. More advanced methods and in vivo studies are needed to better understand the effects of NMOR on the organism and XO enzyme