Figure 2. Saturation curves of the α₂βγ heterotetramer and the αβ and αγ heterodimers for isocitrate in the absence and presence of positive regulator(s).

(a) Saturation curves of the α₂βγ enzyme. (b) Saturation curves of the αβ enzyme. (c) Saturation curves of the αγ enzyme. The activities of the α₂βγ and αγ enzymes were measured at the standard conditions (33 mM Tris-acetate, pH 7.4, 2 mM MnCl₂, and 3.2 mM NAD) with varied concentration of ICT in the absence or presence of 1 mM CIT or/and 1 mM ADP. The activity of the αβ enzyme was measured at the standard conditions but with higher concentration of Mn^2 +(50 mM). The derived V_max, S_0.5 and k_cat are listed in Tables 2 and 3.