Table 3.

Subunit ratios of the enzyme from SDS-PAGE and the enzymatic activities of the heterotetramer at 25 ºC

Enzyme	Subunit ratios (Non-His-tag: His-tag)	Enzymatic activitiesa
		SAMP (% of WT)		SAICAR (% of WT)
		Emeas	Ecalc	Emeas	Ecalc
WT		100		100
R194C		125		107
L311V	N.A.	90	N.A.	86	N.A.
R396H		20		22
R396C		21		29
non-His-tag WT/His-tag WT
Pool 2	1.3:1	95	100	93	100
Pool 3	1:3.7	95	100	93	100
non-His-tag R396C/His-tag WT
Pool 2	1.2:1	45	50	60	56
Pool 3	1:2.3	100	76	82	79
non-His-tag R396H/His-tag WT
Pool 2	1.1:1	59	57	62	58
Pool 3	1:1.6	102	68	85	69
non-His-tag R396C/His-tag R194C
Pool 2	1.2:1	65	68	64	65
Pool 3	1:3.2	113	100	103	88
non-His-tag R396H/His-tag L311V
Pool 2	1.8:1	57	44	56	45
Pool 3	1:1	85	56	80	54

^aThe activity of each pool for SAMP and SAICAR was measured separately at 25 °C by addition of a 10 μl aliquot of enzyme to 1.0 mL solution containing 50 mM HEPES buffer, pH 7.4 and 60 μM of each substrate. E_calc is the calculated specific activity of each pool relative to that of WT and E_meas is the measured specific activity relative to that of WT. The specific activities of WT enzyme with respect to SAMP and SAICAR are 9.2 and 15 μmol/min/mg, respectively. N.A. = not applicable.