Table 1.

Summary of kinetic parameters

k_basal, ATPase activity in the absence of actin; v_max, maximum actin-activated ATPase activity; K_app, concentration of actin at one-half v_max. v_max and K_app were estimated from hyperbolic fits. v_max (60 μm), actin-activated ATPase rate at 60 μm F-actin; k_cat/K_app, catalytic efficiency; k_−AD^fast and k_−AD^slow, rate constants of the ADP release from acto-myosin; k_−Pi, rate constant of P_i release at 20 μm F-actin concentration.

Parameter	S1f	S1f cgmRLC	S1f MLC2v	S1s	S1s cgmRLC	S1s MLC2B
kbasal (s−1)	0.04 ± 0.01	0.06 ± 0.01	0.04 ± 0.01	0.05 ± 0.01	0.55 ± 0.01	0.04 ± 0.01
vmax (fit) (s−1)	3.5 ± 1	2.5 ± 0.1	1.0 ± 0.3	0.5 ± 0.2	0.6 ± 0.1	0.1 ± 0.1
vmax (60 μm) (s−1)	0.66 ± 0.01	0.52 ± 0.2	0.30 ± 0.02	0.14 ± 0.01	0.62 ± 0.01	0.09 ± 0.01
Kapp (fit) (μm)	278 ± 96	244 ± 10	142 ± 54	208 ± 91	22 ± 3	39 ± 4
kcat/Kapp (10−3 μm−1 s−1)	10	11	4	2	4	2
k−ADfast (s−1)	> 500	> 500	> 500	54 ± 3	61 ± 1	60 ± 3
k−ADslow (s−1)				4 ± 1	5 ± 1	3 ± 1
k−Pi (20 μm) (s−1)	0.18 ± 0.01	0.29 ± 0.01	0.07 ± 0.01	0.05 ± 0.01	0.17 ± 0.01	0.03 ± 0.01