Formation of enzyme-bound carbanion intermediate in the isocitrate lyase-catalyzed reaction: enzymatic reaction of tetranitromethane with substrates and its dependence on effector, pH, and metal ions

Archives of Biochemistry and Biophysics
O P Malhotra, U N Dwivedi

Abstract

Isocitrate lyase of germinating castor seed endosperm catalyzes the reactions of succinate and of isocitrate (but not of glyoxylate) with tetranitromethane (TNM), giving rise to the nitroform anion (C-(NO2)3), analogous to the reaction of TNM with carbanions (O.P. Malhotra and U.N. Dwivedi, 1984, Ind. J. Biochem. Biophys. 21, 65-67). The kinetics of this reaction have been investigated under a variety of conditions. At a fixed TNM concentration, the initial rate of reaction exhibits a hyperbolic saturation of the enzyme with isocitrate. The reaction with succinate, however, shows "negative cooperativity" in succinate saturation and the data are consistent with the existence of two sets of succinate binding sites of unequal affinity ("tight" and "loose" sites). Equal reaction rates are observed at enzyme-saturating concentrations of succinate and isocitrate. In every case, the rate of reaction is proportional to the TNM concentration. In the presence of alpha-ketoglutarate, hyperbolic saturation curves are obtained for all the substrates (TNM and succinate or TNM and isocitrate). In the presence of this effector the Km of succinate and TNM are independent of the concentration of the second substrate. On the other hand, sets of p...Continue Reading

References

May 1, 1977·Archives of Biochemistry and Biophysics·B Subbarao, U W Kenkare
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Dec 1, 1984·Archives of Biochemistry and Biophysics·O P MalhotraU N Dwivedi
Mar 1, 1982·Archives of Biochemistry and Biophysics·O P Malhotra, P K Srivastava
Jun 1, 1983·Archives of Biochemistry and Biophysics·A S Bhagwat, B A McFadden

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Citations

Jan 1, 1990·Comparative Biochemistry and Physiology. B, Comparative Biochemistry·P VanniB A McFadden

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