FORMATION OF FUSIDIC ACID-G FACTOR-GDP-RIBOSOME COMPLEX AND THE RELATIONSHIP TO THE INHIBITION OF GTP HYDROLYSIS

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  • OKURA AKIRA
    Institute of Applied Microbiology, University of Tokyo Present address : Bahyu Pharmaceutical Co., Ltd.
  • KINOSHITA TADATOSHI
    Institute of Applied Microbiology, University of Tokyo
  • TANAKA NOBUO
    Institute of Applied Microbiology, University of Tokyo

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Fusidic acid increases the binding of GTP with ribosomes and G factor. GTPis hydrolyzed to GDPin the complex with or without the antibiotic. Fusidic acid binds with G factor in a molar ratio of 1: 1 with an association constant 1.2×105M-1. The binding is strongly stimulated by ribosomes and GTP. Formation of fusidic acid-G factor-GDP-ribosome complex is demonstrated by equilibrium dialysis and ultracentrifugal separation methods. Measurements of binding at equilibrium indicate a stoichiometric combination of thefoursubstances in a molarratio of 1: 1: 1: 1, provided that half of the ribosomes employed are active in this function. The association constant of fusidic acid is 2.2×106 M-1. Less binding of the antibiotic is observed when fusidic acid-resistant G factor is used. A significant binding of fusidic acid is demonstrated when 70S ribosomes are replaced by 50S ribosomes or when GDP is used instead of GTP. Ki value for fusidic acid is 106M in the GTPase reaction. It is in accordance with the association constant in the complex formation.

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