Determinatton of Equilibrium and Kinetic Constants for the Interaction of GTPases with Nucleotides, Regulators and Effectors

GTP-binding proteins constitute a class of proteins which are involved in signal transduction and regulation of many processes in the cell. They are, in general, GTPases. The basis of their action is that they have different properties with respect to their interactions with partner molecules, depending on whether GDP or GTP is bound to the active site. Since the GTPase properties of these proteins differ from those of proteins whose main role is catalytic, i.e., whose essential purpose is to convert one or more substrates into one or more products, often at the highest possible rate, the standard steady state methods used to investigate the kinetic properties of such enzymes cannot normally be employed in the investigation of GTPases. The reasons for this, for most members of the class, are the very tight binding of guanosine nucleotides combined with the slow or very slow spontaneous rate of GTP cleavage on the protein.