Ligand-modulated cross-bridging of microtubules by phosphofructokinase.

The interaction of phosphofructokinase and microtubules results in mutual effects: decreases overall activity of the kinase and alters the ultrastructural organization of microtubules. Electron microscopic studies provide direct evidence for the periodical cross-bridges of microtubules by the kinase. 3-4 closely aligned tubules are connected by rows of highly periodic lateral arms about 13 nm long and 12 nm wide. The bundling activity of the enzyme seems to be specific since aldolase, which also interacts with microtubules, does not cross-link tubules, but it impedes the binding of the kinase to tubules. ATP, ADP and fructose bisphosphates inhibit the cross-bridges of microtubules by phosphofruktokinase to a different extent and concentration dependent manner. The kinase complexed with specific metabolites inducing distinct conformers does not interact with tubules. Microtubules cross-linked by the kinase became partly resistant to the depolymerizing action of vinblastine.