PROTEINS OF AXONAL TRANSPORT: INVESTIGATION OF SOLUBILITY CHARACTERISTICS AND BEHAVIOUR IN GEL FILTRATION

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Abstract
Rapid axonal transport of proteins in retinal ganglion cells of the rabbit was studied following intraocular injections of labeled amino acids. Approximately 10% of the transported radioactivity was found in the supernatant following homogenization and high speed centrifugation of the nerve terminal region. Relatively simple manipulations with ionic strength, pH and the presence of a chelating agent could solubilize an equivalent amount of radioactivity from the pellet. Lithium diiodosalicylate solubilized most rapidly transported membrane proteins. Gel filtration of readily soluble rapidly transported radioactivity gave a main macromolecular radioactive peak with an approximate MW of 500,000 dalton as determined on Sephadex G-200. Gel filtration on Sepharose CL-6B gave a MW of about 160,000 for the same radioactive peak. SDS [sodium dodecylsulfate] polyacrylamide gel electrophoresis of rapidly transported soluble proteins and fractions derived from these proteins via gel filtration and ion exchange chromatography revealed in all cases a very complex picture of labeled polypeptides. Rapid axonal transport of soluble proteins in this system seems to involve many different macromolecules.