||See related bionumbers giving higher values of 10^9-10^11 as the theoretical diffusion limit in water. P.207 right column top paragraph: "There is an upper limit to Kcat/Km, imposed by the rate at which E and S can diffuse together in an aqueous solution. This diffusion controlled limit is 10^8 to 10^9 M^-1×s^-1, and many enzymes have a kcat/Km near this range (Table 6–8). Such enzymes are said to have achieved catalytic perfection. Note that different values of kcat and Km can produce the maximum ratio." In Berg et al, 1981 PMID 7317363, the one-step diffusion-controlled interaction of lac repressor (R) with lac operator (0) is calculated to be 10^7 - 10^8 1/(M×sec) (see pp. 6930 in article). See BNID 105087. See Wang et al., 2013 PMID 23262491 p.175 left column top paragraph: "Despite this, no promoter-association rate exceeding the 3D-diffusion limit (~10^8–10^9 M^−1×s^−1) has ever been reported [refs 27, 28], and the potential contribution of facilitated diffusion to the promoter search process has been challenged in the literature [ref 29]."