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. 2007 Nov 2;94(4):1412–1427. doi: 10.1529/biophysj.107.111096

FIGURE 2.

FIGURE 2

Mechanism proposed for DADH catalysis. E represents the enzyme, and BH represents an ionizing group with a pKa value of 7.1 and 7.3 in DlADH at 23.5°C and 19.0°C, respectively (27,71), and 7.6 in DmADHS (slow alleloenzyme) at 23.5°C (28,30). The insert shows the variation of Φ2 with varying pH for DlADH at 19.0°C, where Φ2 = (1/k2)(1 + (k−2/k)(1 + (k′/k′−2))) and the kinetic constants are those in Scheme 1. It was shown that only k2, i.e., the kon velocity for the alcohol, varied with pH, and hence Φ2 = Φ*2 (1 + ([H+]/Ka)). The theoretical curve is based on a pKa of 7.3 and a Φ*2 of 2.0 mMs.