Data is presented suggesting that Slow Component a (SCa) of axonal transport involves the movement along microtubules of an insoluble complex of tubulin, neurofilament, spectrin, and other proteins. These structures have been given the provision acronym "SCAPs." The goal of this research is to gain a fuller understanding of these structures. The protein composition of highly purified SCAPs will be analyzed by routine biochemical and immunochemical approaches. A microtubule-stimulated ATPase is present in SCAP preparations, which appears to be responsible for the in vitro phenomenon of microtubular gelation-contraction. This ATPase activity will be characterized biochemically, with the goal of identifying and understanding the action of the enzyme(s) involved. The properties of this ATPase activity and its relationship to microtubule gelation-contraction in vitro (and possibly to SCAP movement in vivo) will be analyzed. These experiments will provide significant new information relevant to the validity of the hypothesis that SCa involves the translocation of SCAPs along microtubules.
