# Calculating a Kis value for a competitive inhibitor

1. Mar 18, 2005

### gravenewworld

Say you are given the velocity of a reaction catalyzed by an enzyme and associated concentrations of substrate, but there is also a competitive inhibitor present. To find Vmax and Km for the reaction you would plot the reciprocal plot of the Mekelis(sp?)-Menton Equation and estimate the Y and X intercepts. My question is, I know that if you plot the slope of the reciprocal plots of the MM equation vs. different concentrations of inhibitor you can find the Kis value for the enzyme inhibitor complex from the x intercept of this plot. Is the Kis value = -(the x intercept) or is -(1/Kis)=x intercept?

Last edited: Mar 19, 2005