Table 1.

Glycosyltransferase activity of various HvGBSSIa variants in vitro

Enzymec	ADP-Glca			Glycogenb
	k cat	K m	k cat/Km	k cat	K m	k cat/Km
	(min–1)	(µM)	(min–1 µM–1)	(min–1)	(µg ml–1)	(min–1 µg–1 ml)
HvGBSSIaWT	5.8 ± 0.2	160 ± 15	3.65 × 10–2 (100%)	6.3 ± 0.2	72 ± 6	8.69 × 10–2 (100%)
HvGBSSIaD219V	2.76 ± 0.06	127 ± 9	2.17 × 10–2 (59%)	3.2 ± 0.2	84 ± 16	3.81 × 10–2 (44%)
HvGBSSIaM490V	21.2 ± 0.6	71 ± 7	2.99 × 10–1 (818%)	19.4 ± 0.8	159 ± 20	1.22 × 10–1 (140%)
HvGBSSIaI491V	6.7 ± 0.3	114 ± 15	5.88 × 10–2 (161%)	6.5 ± 0.3	108 ± 15	6.02 × 10–2 (69%)
HvGBSSIaM490V/I491V	0.94 ± 0.04	56 ± 8	1.70 × 10–2 (47%)	1.3 ± 0.2	175 ± 77	7.43 × 10–3 (9%)
HvGBSSIaCDC Alamo	0.56 ± 0.03	51 ± 10	1.09 × 10–2 (30%)	0.7 ± 0.1	139 ± 62	5.30 × 10–3 (6%)

^a ADP-Glc as the varying substrate; the concentration of rabbit liver glycogen was constant at 1 mg ml^–1.

^b Rabbit liver glycogen as the varying substrate; the concentration of ADP-Glc was constant at 1 mM.

^c Wild-type k_cat activities correspond to 0.102–0.095 µmol min^–1 mg^–1.