So KCAD, the turnover number, tells us how many substrate molecules are transformed into product molecules by single active side per unit time, usually per second. Now? What about Km? Well, Km has two meanings. One meaning of the Km basically tells us it's the substrate concentration that gives us rate of VMAX divided by two. But the other meaning of Km, basically Km describes how attracted that enzyme the active side is to that substrate.