Apparently irreversible GTP hydrolysis attends tubulin self-assembly

The pathway of GTP hydrolysis associated with microtubule polymerization was investigated using an assay of intermediate 18O-exchange reactions. Under a variety of conditions influencing tubulin self-assembly, GTP was hydrolyzed without any evidence of multiple reversals characteristic of reversible phosphoanhydride-bond cleavage. These results also accord with published findings that ATP hydrolysis during actin polymerization fails to display intermediate exchange reactions [Carlier, M. F., Pantaloni, D., Evans, J. A., Lambooy, P. K., Korn, E. D. and Webb, M. R. (1988) FEBS Lett. 235, 211-214].