Axonal microtubules of crayfish and spiny lobster nerve cords are decorated with a heat-stable protein of high molecular weight.

Axons of crayfish and spiny lobster ventral nerve cords contain large numbers of microtubules that are decorated with fine filaments. These microtubules can be stabilized in permeabilized axons using buffers that contain either polyethylene glycol or glycerol/dimethyl sulphoxide. In the former, the stabilized microtubules retain their filaments and their normal spacing; in the latter, the filaments are stripped off and the bare microtubules collapse onto one another. This observation has been used as the basis for a method of identifying some of the proteins that make up the filaments. Axons are first permeabilized and stabilized in either buffer and then treated with a microtubule-depolymerizing buffer. The axons treated first with polyethylene glycol release tubulin and significant quantities of microtubule-associated proteins (MAPs), while the axons pre-treated with glycerol release tubulin and only traces of associated proteins. One of the proteins released in largest quantity along with tubulin from polyethylene glycol-treated axons is a high molecular weight, heat-stable MAP that co-electrophoreses with MAP-2 from mammalian brain. This same protein co-purifies with tubulin that is obtained from crayfish nerve cords by two cycles of polymerization and depolymerization. It is concluded that this protein is a component of the filaments that decorate the axonal microtubules of the crayfish and spiny lobster.