Hexokinase I activity was determined spectrophotometrically at 25 °C by the method of coupling the glucose-6-phosphate production via glucose-6-phosphate dehydrogenase with the change in the absorbance of NADPH at 340 nm and as described by [66]. The reaction was started by the addition of purified brain hexokinase I (0.24 μg) (gift from J. Wilson) to 1.0 ml of reaction mixture containing 0.05 M Tris-HCl (pH 8.5), 7.4 mM MgCl2, 6.6 mM ATP, 0.65 mM NADP, 11.1 mM monothioglycerol, and 1 unit of glucose 6-phosphate dehydrogenase. In the case of hexokinase activity measured in the presence of Cox11 and LD, the purified HKI was incubated with the recombinant proteins for 15 min at 4 °C before measurement of the activity. The data were fitted directly into the Michaelis-Menten equation using SIGMAPLOT (SPSS Science).