Apparently irreversible GTP hydrolysis attends tubulin self‐assembly

Abstract
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].