Figure 2

Substrate inhibition of phosphofructokinase II (encoded by pfkB) from E. coli. a Substrate saturation curve. Phosphofructokinase activity was determined by following the decrease in the NADH concentration using aldolase, triose phosphate isomerase and glycerol 3-phosphate dehydrogenase as coupling enzymes. The reaction was started by the addition of phosphofructokinase, and the decrease in absorbance at 340 nm was recorded. a Substrate saturation curves. Points were experimental data and lines were theoretically drawn from Eq. (1), using the following parameter values: V _max  = 110 μmol/min per mg. K _m  = 0.065 mM. Curve 1 \(K_{i}^{\prime }\) = 0.65 mM. Curve 2 \(K_{i}^{\prime }\) = 2.8 mM. Curve 3 \(K_{i}^{\prime }\) = 7 mM. b Quotient velocity plot. c Reciprocal of the quotient velocity plot. \(K_{i}^{\prime }\) values were calculated from the slope of the lines at the higher substrate concentration.