Table 1.

Summary of the rate constants and extents for the interaction of nucleotides with wild-type and salt-bridge mutant HMMs

Measurements	Parameters	Wild-type	R247A	R247E	E470A	E470R	R247E/E470R
MantATP binding	Fast, %	100	82	93	87	58	91
	K1k+2 (s−1⋅M−1)	3.5 × 105	0.49 × 105	0.28 × 105	4.5 × 105	5.7 × 105	2.2 × 105
	Slow, %					33
	kslow, s−1					0.0001
Trp fluorescence	Increase, %	19	1.8	1.1	16	4 (6.7)	15
	K1k+2 (s−1⋅M−1)	2.5 × 105	0.33 × 105	0.23 × 105	3.1 × 105	4.5 × 105	1.6 × 105
	kmax, s−1	166			92		172
	K0.5, μM	650			330		980
Phosphate burst	Mole per mole of HMM head	0.68	0	0	0	0	0
MantATP release	k+3 or k+3k+4/(k+3 + k−3), s−1	0.009	0.003	0.0011	0.00014	0.000036	0.001
MantADP release	k+5, s−1	1.3	0.027	0.0036	0.28	0.34	0.031
Steady-state ATPase	kcat, s−1	0.005	0.002	0.0005	0.00008	0.00003	0.0004
Actin-activated ATPase	kmax, s−1	1.9	0	0	0	0	0
	Kactin, μM	120

^*Conditions: 0.45 M KCl, 3 mM MgCl₂, 1 mM EDTA, 20 mM Tris⋅HCl (pH 7.5) at 20°C.

^† The estimated increase for E470R of which sites are vacant.

^‡ Conditions: 200 μM F-actin, 0.04 mM KCl, 2 mM MgCl₂, 20 mM Tris⋅HCl (pH 7.5) at 25°C.