Table II. Kinetic properties of recombinant smooth muscle myosin light chain kinases.

Recombinant and mutant smooth muscle myosin light chain kinases were expressed in COS cells, and activities were measured in lysates for the various kinetic parameters as described under “Materials and Methods.” The values are means ± S.E. for three to six experiments.

Kinase	Ca2+/CaMa	EGTAa	[Ca2+]0.5b	KCaMc
	pmol/min/ng		μm	nm
Wild-type	28.8 ± 3.1	0.0	0.66 ± 0.04	1.0
R967A	18.9 ± 1.9	0.0	0.36 ± 0.02	0.25 ± 0.02
K965A	15.8 ± 1.3	0.0	0.24 ± 0.02	0.11 ± 0.03
K965A-R967A	8.6 ± 1.2	0.0	0.12 ± 0.01	0.04 ± 0.01
D966K	51.6 ± 7.6	0.0	0.56 ± 0.03	0.71 ± 0.16
D966A	42.7 ± 2.9	0.0	0.78 ± 0.05	1.5 ± 0.27

^aThe specific activities measured in the presence of Ca²⁺/calmodulin or EGTA are expressed as pmol of ³²P incorporated/min/ng of kinase.

^bThe concentration of Ca²⁺ (μm) required for half-maximal activation of smooth muscle myosin light chain kinase.

^cK_CaM values (nm) were calculated from the data presented in Fig. 4 as described under “Materials and Methods.”