Effect of 6-hydroxydopamine on polymerization of tubulin. Protection by superoxide dismutase, catalase, or anaerobic conditions.

Microtubular protein (tubulin) isolated from porcine brain was subjected to selected oxidative stresses, including incubation with the neurotoxin 6-hydroxydopamine (6-OHDA) under aerobic and anaerobic conditions. The functional capacity of the tubulin was determined on the basis of its ability to form microtubules as measured by alterations in the viscosity of the test mixtures, and confirmed by electron microscopy. 6-OHDA completely inhibited formation of microtubules at concentrations as low as 10 mM. Assembled microtubules were half as susceptible to destruction by 6-OHDA as unaggregated tubulin. Anaerobic conditions or the presence of catalase, superoxide dismutase, or a mixture of superoxide dismutase and catalase provided partial protection against 6-OHDA-induced destruction. In control reactions, tubulin-containing solutions incubated for up to 8 hr at ambient oxygen tensions, also showed significant decreases in ability to polymerize. Anaerobic conditions provided partial protection against this loss of function. In contrast, ascorbate accelerated the loss of activity upon standing, while glutathione or dithiothreitol offered no protection.