TABLE 2.

Kinetic parameters of purified xylose dehydrogenase from H. marismortui^a

Substrate	Vmax (U/mg)	Km (mM)	kcat (s−1)	kcat/Km (s−1, 102)
d-Xyloseb	107	1.2	356	2.97
d-Ribosec	108	2.3	360	1.57
d-Glucosed	82	64	273	0.043
d-Galactosee	39	NDh
d-Fructosef	2	ND
d-Arabinoseg	1	ND

^aEnzyme activity was measured at 37°C with 0.1 M Tris-HCl (pH 8.3)-1.5 M KCl.

^bConcentrations under V_max conditions: d-xylose, 10 mM; NADP⁺, 1 mM.

^cConcentrations under V_max conditions: d-ribose, 10 mM; NADP⁺, 1 mM.

^dConcentrations under V_max conditions: d-glucose, 100 mM; NADP⁺, 1 mM.

^eConcentrations under V_max conditions: d-galactose, 100 mM; NADP⁺, 2 mM.

^fConcentrations under V_max conditions: d-fructose, 100 mM; NADP⁺, 2 mM.

^gConcentrations under V_max conditions: d-arabinose, 100 mM; NADP⁺, 2 mM.

^hND, not determined.