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The minor form of phosphofructokinase (EC 2.7.1.11; PFK), which was suggested to be of plastid origin from the host fraction of chickpea nodules, was isolated as a small protein with apparent molecular mass near 220 kDa and purified to a high degree. SDS-PAGE and western blot indicated that the enzyme was made up of a homotetrameric structure (55 kDa). The enzyme had sharp pH profiles with maximal activities at pH 8 and displayed Michaelis-Menten kinetics with respect to Fru-6-P and nucleoside triphosphate substrate at the pH optimum (pH 8) and at pH 7. MgATP was the most effective phosphoryl donor. Phosphoenolpyruvate was a potent inhibitor of minor PFK activity, and the enzyme was also strongly inhibited by 3-phosphoglycerate, 2-phosphoglycerate, and to a lesser extent, PPi. Minor PFK was weakly activated by KCl, NaCl and Pi, and was inhibitory at high concentration of KCl and Pi.
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