Protons and Mg2+ Cations as Probes in Investigating the Role of GTP in Initiation Complex Formation

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Abstract
FMet-tRNAfMet binding to both 30-S subunits and to 70-S particles [from Escherichia coli] is dependent on pH and Mg2+ concentration: for fMet-tRNAfMet binding to 70-S particles, variations of pH and Mg2+ concentration are tightly interdependent. This behavior can be interpreted by the polyelectrolyte theory as a direct consequence of the fact that the binding occurs in a polyanionic microenvironment. The pH-dependent binding to 70-S particles clearly shows the involvement of 2 prototropic groups which appear to be those carrying out GTP hydrolysis, therefore directly linked to initiation complex formation; with a non-hydrolyzable analog to GTP, guanosine 5''-[.beta.,.gamma.-imido]triphosphate, the binding of fMet-tRNAfMet shows much less interdependence between variation of pH and Mg2+ concentration.