TABLE 1.

Calcium activation and GTP inhibition of transglutaminase activity

The activity of transglutaminase was determined at increasing concentrations of Ca²⁺ or GTP as described under “Experimental Procedures.” Activities are reported as the percentage of maximal activity. EC₅₀ for Ca²⁺ activation (Fig. 2A) and IC₅₀ for GTP inhibition (Fig. 2B) were estimated using GraphPad Prism. TG specific activity values at the plateau Ca²⁺ level (5 mm) are also shown. All values are expressed as the means S.E. for at least 3 independent experiments. Significant differences between wt and mutant TG2 are shown.

Protein	Substitution	EC50 (Ca2+)	IC50 (GTP)	TG specific activity
		μm	μm	Units/mg
TG2	wt	86 ± 9	142 ± 24	3.9 ± 0.4
M1a	R262S	258 ± 32a	23 ± 5b	2.8 ± 0.3
M1b	R263S	195 ± 56b	79 ± 15	2.7 ± 0.1b
M1c	K265S	123 ± 13	182 ± 17	3.1 ± 0.1
M2	K202S/K205S	68 ± 4	145 ± 23	3.8 ± 0.3
M3	K598S/K600S/R601S/K602S	136 ± 13	148 ± 26	3.6 ± 0.2
M4	R19S	67 ± 7	254 ± 8b	3.7 ± 0.5
M5	R28S	115 ± 17	64 ± 27	3.4 ± 0.2
M6	R580S	64 ± 3	No inhibition	4.8 ± 0.4
M7	K634S	260 ± 30a	199 ± 36	3.2 ± 0.2

^a p < 0.001.

^b p < 0.05.