TABLE 4.

Weight average molecular masses, as determined by light scattering experiments, for His-tag WT and His tag mutant enzymes

In all cases, the His tag enzyme was in 0.1 m potassium phosphate buffer (pH 6.5), containing 1 mm EDTA. At higher protein concentrations, these His tag mutant enzymes were unstable and tended to aggregate.

Enzyme	Concentration	Molecular mass
	mg/ml	Da
His-WT	0.03	32,900 ± 1,000
	0.06	38,100 ± 300
	0.09	40,500 ± 3,000
	0.15	46,400 ± 5,100
His-T67A	0.05	43,500 ± 3,000
	0.13	47,500 ± 2,500
	0.26	50,000 ± 2,500
His-R70Q	0.02	26,900 ± 2,000
	0.07	25,900 ± 1,700
His-R74Q	0.01	24,700 ± 5,800
	0.04	24,500 ± 2,500
His-D90N	0.01	23,300 ± 500
	0.04	24,300 ± 9,100
His-D94N	0.04	25,400 ± 8,900
	0.07	25,200 ± 1,200