Formation of fusidic ACID-G factor-GDP-ribosome complex and the relationship to the inhibition of GTP hydrolysis

Abstract

Fusidic acid increases the binding of GTP with ribosomes and G factor. GTP is hydrolyzed to GDP in the complex with or without the antibiotic. Fusidic acid binds with G factor in a molar ratio of 1: 1 with an association constant 1.2×105 M-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 molar ratio 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 70 S ribosomes are replaced by 50 S ribosomes or when GDP is used instead of GTP. Ki value for fusidic acid is 10-6 M in the GTPase reaction. It is in accordance with the association constant in the complex formation. © 1971, JAPAN ANTIBIOTICS RESEARCH ASSOCIATION. All rights reserved.