Characteristics of growth-associated polypeptides in regenerating toad retinal ganglion cell axons.

We report here certain properties of three polypeptides that are rapidly transported in greatly increased amounts during the regeneration of toad optic nerves. All three of these growth-associated polypeptides (GAPs) are associated with a membrane(s) with a buoyant density similar to the plasma membrane. Since none of these GAPs are solubilized substantially by washing the membranes in either low or high ionic strength media, they may be "integral membrane proteins. All three GAPs contain a significant number of polar amino acids (judging from their isoelectric points and their rapid electrophoretic migration under their native charge), suggesting that portions of each molecule must extent away from the membrane surfaces. One of these proteins (GAP-50) is a fucosylated glycoprotein. GAP-50 and GAP-43 appear to be transported preferentially to axon tips; GAP-24 may be distributed more uniformly along the axons. GAP-24 has an extremely short half-life (4 to 6 hr), while the maximum half-lives of GAP-43 (2 to 3 days) and GAP-50 (approximately 1 day) are longer. We discuss the relevance of these properties to possible roles for these polypeptides in the control of nerve regeneration.