Monitoring the real-time kinetics of the hydrolysis reaction of guanine nucleotide-binding proteins.

The conversion of guanosine triphosphate (GTP) to guanosine diphosphate (GDP) and inorganic phosphate (Pi) by guanine nucleotide-binding proteins (GNBPs) is a fundamental enzyme reaction in living cells that acts as an important timer in a variety of biological processes. This reaction is intrinsically slow but can be stimulated by GTPase-activating proteins (GAPs) by several orders of magnitude. In the present study, we synthesized and characterized a new fluorescent nucleotide, 2'(3')-O-(N-ethylcarbamoyl-(5''-carboxytetramethylrhodamine) amide)-GTP, or tamraGTP, which is sensitive towards conformational changes of certain GNBPs induced by GTP hydrolysis. Unlike other fluorescent nucleotides, tamra-GTP allows real-time monitoring of the kinetics of the intrinsic and GAP-catalyzed GTP hydrolysis reactions of small GNBPs from the Rho family.