10^6 - 10^7 sec^-1
||Bar-Even A. et al., The moderately efficient enzyme: evolutionary and physicochemical trends shaping enzyme parameters. Biochemistry. 2011 May 31 50(21):4402-10. doi: 10.1021/bi2002289. p.4402 right column top paragraphPubMed ID21506553
|| enkovic, S. J., and Hammes-Schiffer, S. (2003) A perspective on enzyme catalysis. Science 301, 1196 – 1202.  Hammes, G. G. (2002) Multiple conformational changes in enzyme catalysis. Biochemistry 41, 8221 – 8228.PubMed ID12947189, 12081470
||"Here [investigators] describe a global view of enzyme parameters
with the aim of highlighting the forces that shape the catalytic
efficiency of enzymes."
||"There are also several known physicochemical constraints that set boundaries to kinetic parameters. [refs 15,16] For example, theoretical limitations suggest that kcat is unlikely to be higher than 10^6-10^7S^-1. [primary sources] Furthermore, the apparent second-order rate for a diffusion-limited enzyme-catalyzed reaction with a single low-molecular mass substrate (kcat/KM) cannot exceed ~10^8-10^9S^-1M^-1. [refs 18,19]"