Table 5. Kinetic parameters of the mutant holoenzyme.

Enzyme	Specific activity	No activators				CIT+ADP
		Vmax, ICT	S0.5,ICT	kcata/S0.5,ICT	Hill coefficient for ICT	Vmax, ICT	S0.5,ICT	kcat/S0.5,ICT	Hill coefficient for ICT
	μmol/mg/min	μmol/mg/min	mM	s−1 mM−1		μmol/mg/min	mM	s−1mM−1
αβαγ	20.2 ± 0.3	20.0 ± 0.1	2.35 ± 0.05	11.36 ± 0.04	2.0 ± 0.1	21.3 ± 0.4	0.163 ± 0.007	174 ± 3	1.5 ± 0.1
αY126Fβ	0	NDc	ND	ND	ND	ND	ND	ND	ND
αY126Fγ	0	ND	ND	ND	ND	ND	ND	ND	ND
αY126FβαY126Fγ	0	ND	ND	ND	ND	ND	ND	ND	ND
αβαY126Fγ	8.45 ± 0.14	8.47 ± 0.42	2.12 ± 0.13	5.32 ± 0.13	1.6 ± 0.1	8.43 ± 0.32	0.148 ± 0.005	75.9 ± 5.1	1.4 ± 0.1
αY126Fβαγ	9.00 ± 0.15	9.07 ± 0.39	2.41 ± 0.12	5.02 ± 0.12	1.7 ± 0.1	9.12 ± 0.39	0.129 ± 0.006	94.2 ± 3.0	1.3 ± 0.1
αβαγK151Ab	1.76 ± 0.11	8.24 ± 0.59	21.9 ± 1.1	0.501 ± 0.035	1.0 ± 0.1	8.02 ± 0.42	17.6 ± 1.5	0.607 ± 0.032	1.0 ± 0.1

The V_max,ICT and S_0.5,ICT in the absence or presence of both 1 mM CIT and 1 mM ADP were determined at the standard conditions with varied concentrations of ICT, except for those noted specifically.

^aA molecular mass of 80 kDa was used to calculate the mole of enzyme in heterodimeric form per mg of protein (1.25 × 10⁻⁸ mol of dimeric enzyme/mg of protein).

^bThe mutant αβαγ_K151A enzyme has the S_0.5,Mn and S_0.5,NAD of 5.10 ± 0.46 mM and 1.54 ± 0.27 mM, respectively, which are much higher than those of the wild-type enzyme. Thus, the V_{max, ICT} and S_0.5,ICT were determined at higher concentrations of MnCl₂ (50 mM) and NAD (10 mM).

^cND: not detectable.