Well, the reason that the Km remains constant is because the inhibitor, by binding onto that enzyme, even though it changes the shape of the active side of the enzyme, and so it changes the efficiency, the Kcat value of that enzyme, it does not change the likelihood that that particular substrate is going to bind onto the active side. So it doesn't matter if the inhibitor is bound to that enzyme or not. In either case, the substrate will have no problem actually binding onto that active side. So we see that in this particular equation, if we have the inhibitor bound onto that enzyme, the substrate is just as likely to bind onto that enzyme as it is to bind onto that enzyme in the absence of that inhibitor. So this reaction takes place just as likely as this reaction takes place. And because of that, the affinity of that particular substrate for the active side does not change.