TABLE 1.

Kinetic parameters for Na⁺ activation in the presence and absence of 50 mm K⁺

Enzyme	Parameter value
	No K+a		50 mm K+
	V1	Ka	V1	Ka	Ki
	μmol/min/mg	mm	μmol/min/mg	mm	mm
Ac-PPase*	0.04 ± 0.01	23 ± 5	0.17 ± 0.01	0.43 ± 0.04	NAb
Ctet-PPase*	0.24 ± 0.01	27 ± 2	0.80 ± 0.08	0.45 ± 0.08	NA
Da-PPase*	0.48 ± 0.08	80 ± 2	0.78 ± 0.09	1.9 ± 0.4	NA
Cl-PPase*	0.26 ± 0.04	14 ± 3	1.1 ± 0.1	0.036 ± 0.002	100 ± 20
Cl-PPase(E242D)*	0.38 ± 0.08	190 ± 50	0.81 ± 0.06	16 ± 2	400 ± 110
Fj-PPase	0.09 ± 0.01	9 ± 2	0.99 ± 0.04	NA	130 ± 20
Lb-PPase	0.14 ± 0.02	9 ± 2	0.46 ± 0.05	NA	NA

^a The K_i value was above 1000 mm in the absence of K⁺.

^b NA, not attendant.