Table 3 Kinetic parameters of the α2βγ, αβ and αγ enzymes in the presence of positive regulators.

From: The β and γ subunits play distinct functional roles in the α2βγ heterotetramer of human NAD-dependent isocitrate dehydrogenase

Enzyme

+CIT

+ADP

+CIT+ADP

V max,ICT

S 0.5,ICT

Hill coefficient for ICT

V max, ICT

S 0.5, ICT

Hill coefficient for ICT

V max,ICT

S 0.5,ICT

Hill coefficient for ICT

k cat a

k cat /S 0.5,ICT

μmol/mg/min

mM

μmol/mg/min

mM

μmol/mg/min

mM

s −1

s −1 mM −1

α2βγ

20.7 ± 1.3

1.27 ± 0.06

1.5 ± 0.1

22.1 ± 0.3

0.868 ± 0.021

2.0 ± 0.1

21.3 ± 0.4

0.163 ± 0.007

1.5 ± 0.1

28.4 ± 0.5

174 ± 3

αβ

11.2 ± 0.4

12.1 ± 1.1

1.1 ± 0.1

11.2 ± 0.3

12.1 ± 1.1

1.0 ± 0.1

11.9 ± 0.3

12.6 ± 0.8

1.2 ± 0.1

15.8 ± 0.4

1.25 ± 0.03

αγ

10.0 ± 0.2

2.61 ± 0.12

1.2 ± 0.0

9.42 ± 0.09

1.69 ± 0.05

1.6 ± 0.1

13.1 ± 0.4

0.182 ± 0.015

1.0 ± 0.0

17.6 ± 0.5

96.7 ± 2.7

  1. The Vmax,ICT and S0.5,ICT of the α2βγ and αγ enzymes in the presence of 1 mM CIT or 1 mM ADP or both were determined at the standard conditions with varied concentrations of ICT. The Vmax,ICT and S0.5,ICT of the αβ enzyme were determined at the same conditions but with higher concentration of MnCl2 (50 mM) and varied concentrations of ICT.
  2. 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).
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