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Updated: Jun 26, 2026

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes
Published on: January 16, 2016
Cooperativity of two active sites in bacterial homodimeric aconitases
Daisuke Tsuchiya1, Nobutaka Shimizu, Masaru Tomita
1Institute for Advanced Biosciences, Keio University, 403-1 Nipponkoku, Daihoji, Tsuruoka, Yamagata 9970017, Japan. dsktcy@ybb.ne.jp
Abstract:
Aconitase catalyzes a reversible isomerization of citrate into isocitrate in the Krebs cycle. Escherichia coli possesses two kinds of aconitases, aconitase A (AcnA) and B (AcnB), whose structural organizations are different. We analyzed the structural state of AcnA by the chemical crosslinking and small-angle X-ray scattering. The protein adopts a homodimer in solution, as AcnB does. The catalytic assay of the two aconitases revealed that the isomerization of isocitrate displayed a negative cooperativity of the two active sites within each homodimer. On the other hand, insignificant cooperativity was observed in the reverse reaction. Therefore, the homodimerization of AcnAB yields a substrate-dependent cooperative effect. In conjunction with the dissociable homodimer of AcnB, the catalytic property could affect the intracellular metabolic process involving the Krebs cycle.
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