PMID: 2632362Dec 1, 1989

Site-site heterogeneity in isocitrate lyase of castor seed endosperm: evidence from kinetics of inactivation by tetranitromethane

Indian Journal of Biochemistry & Biophysics
U N Dwivedi, O P Malhotra

Abstract

Inactivation of isocitrate lyase (native and EDTA-dialysed) by excess tetranitromethane (TNM) exhibits, biphasic kinetics, in which half of the initial activity is lost in a fast and the remaining half in a slow phase each following the pseudo-first order kinetics. Rate constants of the two phases are proportional to the TNM concentration. High succinate concentration protects the enzyme against TNM inactivation only in the slow phase without any effect on the fast phase. With the EDTA-dialysed enzyme, no such protection (against inactivation by TNM) is observed in the presence of succinate or Mg2+ ions. Addition of both these ligands together brings about protection against the slow phase (as with the native enzyme). It has been proposed that the site-site heterogeneity of isocitrate lyase is a consequence of its quaternary structure constraints.

Related Concepts

Castorbean Seed
Methane
Oxo-Acid-Lyases
Pseudo brand of pseudoephedrine
Plants, Toxic
Succinates
Ricinus plant
Succinate
Ricinus communis
Edetic Acid

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