STUDIES ON UREA BIOSENSORS BASED ON IMMOBILIZED CORYNEBACTERIUM-GLUTAMICUM AND THEIR KINETIC RESPONSE PROCESSES

Two novel biosensors for urea based on immobilized corynebacterium glu tamicum 617 and corynebacterium glutamicum ATCC13032 in calcium algina te gel coupled with an ammonia gas-sensing electrode, were designed an d constructed. Calibration plots of measured potential difference (mV) vs. log of urea concentration were linear in the range of 5.6 x 10(-5 )-1.4 x 10(-2) and 5.6 x 10(-5)-1.1 x 10(-2) mol l(-1), with slopes of 59.2 and 61.3 mV per decade respectively, in pH 8.0, 0.1 mol l(-1) ph osphate buffer solution at 30 degrees C. The relationship between the initial response velocity and the substrate concentration was also dis cussed. The results indicate that the kinetic response process of the reaction catalyzed by bacteria is similar to that by isolated enzyme. Using an Eadie-Hofstee plot, the apparent Michaelis constant K-m and t he maximum initial response velocity V-m for urease in the immobilized bacterial membrane were determined. The two urea biosensors were succ essfully applied for the actual measurement of urea in urine and were relatively stable for 20 and 40 days respectively.