The enzyme reaction was conducted at 37°C in a temperature-controlled quartz cuvette, and the absorbance of NADH was recorded at 340 nM in a Milton Roy (Rochester, NY) spectrophotometer. After recording of the background rate of NADH oxidation for 5 min without samples, 10 ^l of supernatant was added to the reaction mixture and mixed, and the rate of NADH oxidation was recorded at 1-min intervals for 5 min. The linearity of NADH oxidation throughout the recording duration indicated that the fall in absorbance was not due to substrate limitation. The enzyme activity was expressed as millimoles NADH oxidized per minute per milligram protein. antibiotics levaquin
Determination of PK Activity
PK activity was determined essentially as described by Valentine and Tanaka with modification to fit 1-ml reaction volume. The pyruvate kinase reaction is a secondary control point in glycolysis, controlling the transfer of the high-energy phosphate group from phosphoenolpy-ruvate to ADP. It is an allosteric enzyme, and under the intracellular condition, PK reaction is essentially irreversible. Because intracellular ATP concentration negatively influences PK activity, increased ATP utilization due to heightened cellular activity will result in enhanced PK activity.