Nesheim [1] showed how heparin, a common ingredient in blood-thinning medicines, catalyzes and changes the rate law of the antithrombin III-thrombin binding reaction. This is summarized by three equations that represent the observed rates for catalysis. The reaction can be modeled by a piecewise function showing three possible reaction orders in the catalysis by heparin. You can vary the sliders for the combined mass of antithrombin III and thrombin and the rate order for different amounts of added heparin.