KINETICS STUDIES ON NITRATE REDUC-r ASE FROM MILLET

Abstract

Millet seedlings (Ex-Borno, Gero type) were grown and crude cell extract of the leaves was used to assay for the activity of Nitrate reduCtase (EC 1.6.6.1) spectrophotometrically at 540 nm according to Neyra and Hageman method (1975). Michealis-menten constant, km, and maximum velocity, Vmax, were found to be 106.55 pM and 15.18 umote min" gram·' tissue respectively. Optimum temperature was found to be 35 DC,while optimum pH was 6.5. The activation energy ot the reaction was 38.29 KJ mote", Glutathione was found to inhibit the enzyme competatively with ki of 2.33 x to: pM. Residual activity rate constant at 30°C, 40°C and 50°C were 3x1~ min", 6 x 10-3 min" and 9 x 10-3 min" and the biological half life of the corresponding temperatures were 231.0 , 115.5 and 77.0 minutes respectively. Activation energy between 30°C and 40 °C was 25.027 KJ mot' and for40DC and 50DC it was 292.805 J mot', The enthalpy of ectivetion, H* was 22.508 KJ mot' K' and enthropy S· was -218.27 Jmot' 1\'. The free energy ~as 88.642 KJ mot' K'.