Axonal transport of proteins. A new view using in vivo covalent labeling.

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Abstract
The injection of [2,3-3H]n-succinimidyl propionate ([3H]n-SP) into the rat sciatic nerve was used to covalently label intra- and extra-axonal proteins. Extra-axonal proteins (e.g., myelin proteins) remained in the injection site. Intra-axonal proteins were transported in the anterograde and retrograde directions. The mobile labeled proteins apparently moved by normal axonal transport processes since autoradiography showed they were localized exclusively within the axon at considerable distances from the injection site, specific and identifiable proteins (by SDS gel electrophoresis) moved at expected rates in the anterograde direction, and an entirely different profile of proteins moved in the anterograde vs. retrograde direction. This novel approach to axonal transport, which is independent of de novo protein synthesis, provided a unique view of slow anterograde transport and particularly of retrograde transport of endogenous proteins. A large quantity of a 68,000 MW protein, moving at .apprx. 3-6 mm/day, dominated the retrograde transport profile. [3H]n-SP represents a new and unique vital stain for cell biology.