Distribution and Formation of Isocitritase

Abstract

A NEW reaction of tricarboxylic acids, and the possibility of an alternate oxidative pathway, was indicated by the demonstration by Campbell, Smith and Eagles¹ of glyoxylate formation from citrate by extracts of Pseudomonas aeruginosa. By a preliminary fractionation of the pseudomonad extract, particularly by the removal of aconitase, Smith and Gunsalus² demonstrated the stoichiometry of the reaction as: and showed that this enzyme system, which we termed ‘isocitritase’, required magnesium ion and a mercapto compound as activators. Also following the lead of Campbell, Smith and Eagles, Saz³, although he did not separate the aconitase from the pseudomonad extracts, has concluded from reaction-rates that isocitrate is the substrate, and from inhibitor data and stimulation by yeast kochsaft that both organic and inorganic activators are required. Olson⁴ has also recently reported glyoxylate formation from tricarboxylic acids by Penicillium chrysogenum and other fungi, including baker's yeast, by what appears to be an isocitritase mechanism.