This restriction also pertains to enzymes having more complex reac. tion pathways than that of equation 14. Their maximal catalytic rate when substrate is saturating, denoted by kcat, depends on scvcral rate constants rather than on 3 alone. The pertinent parameter for these enzymes is Rcat/KM. In fact, the heat/Km ratios of the enzymes carbonic anhydrase, acetylcholinesterase, and triosephosphate isomerase are between 108 and 10 Ms, which shows that they have attained kinetic erection. Their catalyic velocily is restricted only by the rale al which ley encounter subslrale in the solution