Kinetics of IMP:NAD+ oxidoreductase in serum of normal Iraqi individuals

The general kinetic parameters of IMP:NAD+ oxidoreductase, were investigated at 37 degrees C in normal human serum. These included substrate - velocity relationship, Km (IMP), Km (NAD), as well as the effect of temperature and pH on the kinetics of the reaction. Optimum conditions of IMP, NAD+ oxidoreductase in serum of normal Iraqi individuals at 37 degrees C were investigated. The optimum IMP concentration was found to be 0.6166 mM and the optimum NAD+ concentration was 6.28 mM, while the optimum pH for the reaction was found to be 8.3. The enzyme shows low stability even when the sera were incubated at low temperature. The activity of the enzyme is proportional to the serum concentration and its optimal temperature for the reaction was 37 degrees C. The enzyme was found to be inhibited by XMP, GMP competitively with Ki values of 0.0724 mM and 0.1583 mM respectively. The inhibition by thyroid hormone (T4) was studied giving a Ki value of 2.25 X 10(-6) mM. The mechanism of enzyme action was found to follow ordered sequential mechanism.