1. Axoplasmic proteins were fractionated by means of Sephadex G-200 chromatography followed by isoelectric focusing. Nine groups of proteins were separated. 2. The binding of colchicine to these groups of proteins was examined and it appeared to associate most strongly with one protein group, of pI value 4.9–5.0, which is the major 14C-labelled component of slow-transport protein. 3. Other fractions also bind colchicine. It is not clear whether these are separate proteins or subunits of the major colchicine-binding fraction.
