Table I. Activity of chimeras and point mutants of Dictyostelium myosin II CM-loop.

Residues in the Sm-loop and Ca-loop that differ from the Wt-loop are in blue; residues in the Ca-loop that differ from both the Sm-loop and Wt-loop are in green. Point mutants are underlined. Capping and development activity are reported as the average of 100 samples. To eliminate one possible source of variation, the same preparation of F-actin was used for all of the assays, which were completed within three days

						ATPase
Loop	Sequence	Dbl. Time	Capping Stage	Develop. Stage	kcat s−1	Kactin μM	kcat/Kactin, s−1μM−1	Motility μms−1
A. Sm and Ca chimeras
Wt	397RILAGRDLVAQ407	12	3	3.9	9	80	0.11	1.4±0.3
Sm	RIKVGRDVVQK	17	3	3.5	10	201	0.05	0.6±0.2
Ca	RVKVGNEYVTK	45	1	1	2	102	0.02	0.4±0.1
Wt-Δ	None	-a	0	0	0.1b	ND	ND	0
Null	-	-a	0	0	-	-	-	-
B. Point mutations in Ca-loop chimera
Ca-1	RVKVGNEVVTK	44	1	1	2	103	0.02	0.5±0.1
Ca-2	RVKVGREYVTK	33	2	1.7	3	147	0.02	0.6±0.1
Ca-3	RVKVGNEYVQK	26	2	2.1	2	102	0.02	0.4±0.1
Ca-4	RVKVGNEVVQK	33	3	2.1	2	112	0.02	0.6±0.1
Ca-5	RVKVGREVVTK	23	3	3	2	171	0.01	0.7±0.1
Ca-6	RVKVGREVVQK	26	3	3.6	3	80	0.04	0.6±0.1
C. Point mutations in Sm-loop chimeras
Sm-1	RILVGRDVVQK	16	3	3.7	5	192	0.03	0.5±0.2
Sm-2	RILVGRDVVQQ	34	3	2.8	3	133	0.02	0.6±0.1
Sm-3	RIKVGRDVVAK	24	3	3.4	2	86	0.02	0.5±0.1
Sm-4	RILAGRDVVQK	13	3	3.8	7	31	0.22	0.5±0.1
Sm-5	RILAGRDVVAQ	14	3	3.9	11	89	0.12	1.5±0.3
D. Ala/Val mutations at position 400
Sm-6	RIKAGRDVVQK	15	3	3.8	9	24	0.38	0.4±0.1
Ca-7	RVKAGNEYVTK	15	3	3.7	11	221	0.05	1.3±0.2
Ca-8	RVKAGREVVQK	15	3	3.8	9	59	0.15	0.8±0.1
Wt-1	RILVGRDLVAQ	36	1	1	1	26	0.04	0.3±0.1
Wt-2	RIKAGRDLVAQ	14	3	3.9	12	141	0.09	1.1±0.1
E. Hypertrophic cardiomyopathy mutations
Wt-3	QILAGRDLVAQ	17	3	3.7	10	285	0.04	1.7±0.3
Wt-4	LILAGRDLVAQ	17	3	3.4	1	195	0.01	0.7±0.2
Wt-5	WILAGRDLVAQ	16	3	3.5	1	176	0.01	0.8±0.2

^aDid not double.

^bATPase activity at 160 μM F-actin; activity too low to determine k_cat and K_actin.