Pyruvate kinase as a microtubule destabilizing factor in vitro

Endogenous control of microtubule dynamism is essential in many cell types. Numerous microtubule-adhering proteins stabilize the polymer status, while very few protein factors are described with opposite effects. The brain- a nd muscle-specific M1 isoform of the enzyme pyruvate kinase is investigated here in this respect. Three pieces of evidence indicate antimicrotubular e ffects of this protein. (1) Pyruvate kinase inhibits taxol-induced tubulin polymerization into microtubules as revealed by turbidimetry. (2) Pelleting experiments show that pyruvate kinase partially disassembles taxol-stabili zed microtubules into less sedimentable oligomers leading to the appearance of tubulin in the supernatant fractions. (3) Electron microscopy reveals t he kinase-induced formation of great amounts of thread-like tubulin oligome rs which tend to accumulate in a light/less sedimentable fraction. Immunoel ectron micrographs using labeled antibody against pyruvate kinase provide e vidence for the binding of pyruvate kinase to the thread-like oligomeric fo rms. The present data allow the assumption that pyruvate kinase may display multiple regulatory functions as a glycolytic control enzyme and as a modu lator of microtubule dynamism. (C) 1999 Academic Press.