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. 2014 Feb 5;53(7):1134–1145. doi: 10.1021/bi4015314

Figure 1.

Figure 1

Full kinetic schemes for ecDHFR and hDHFR. hDHFR rates are shown in bold, and ecDHFR rates are shown in parentheses. Black arrows indicate the major catalytic cycle for both ecDHFR and hDHFR. The minor “upper” cycle, shown by blue arrows, is also used by hDHFR because the release of THF from the product complex is much faster than for ecDHFR. Approximately 35% of the product is channeled through the upper branch by human DHFR. Gray arrows show kinetics involving the apoprotein, E, which do not constitute a significant part of the enzymatic cycle for either protein under cellular conditions. ecDHFR kinetic parameters (25 °C, pH 7) were taken from ref (39), and hDHFR parameters (20 °C, pH 7.65) were taken from ref (14). First- and second-order rates are given in units of s–1 and μM–1 s–1, respectively.