| Comments |
"The spontaneous rates of biological reactions examined in this way span a range of more than 16 orders of magnitude (Figure 4), with half-times ranging from 5 s for the hydration of CO2 [ref 24] to 1.1 billion years for the decarboxylation of amino acids. [ref 25] The active sites of enzymes have evolved to allow these same reactions to proceed at rates that fall within a relatively narrow range, with most kcat values in the neighborhood of 100-1000 s^-1. Thus, enzymes differ enormously in the rate enhancements (kcat/knon) that they produce, ranging from 10^7-fold to 10^19-fold (Figure 5)." |