Table 1.

Functional analysis of mutant GBE proteins.

	Concentration (mg/dl)	A660 average (range)	ΔA660 average	GBE activity (U/mg)
0 min	0	0.998 (0.986–1.01)	–	–
WT-GBE (30 min)	0.25	0.710 (0.705–0.714)	0.289	2.18
Gln46Pro-GBE (30 min)	0.37	0.762 (0.759–0.764)	0.237	1.21
Glu609Lys-GBE (30 min)	0.33	0.796 (0.775–0.817)	0.202	1.15

Each assay was performed in duplicate. Activity (U/mg) = ΔA660/S/T/C/V, where S is the slope of the standard curve; T, reaction time (30 min); C, concentration of GBE protein; V, volume of the GBE protein added (0.01 ml). One unit is defined as the amount of the decrease of 1 mg starch per minute at 37 °C in the reaction mixture. A660 is the spectrophotometric absorbance at 660 nm; ΔA660 is the A660 at 30 min minus the A660 at 0 min.