Tubulin, the basic structural component of microtubules requires nucleotides such as ATP and GTP for its assembly/disassembly process. This process is inhibited by colchicine which strongly interacts with this protein.

Goat brain tubulin was isolated by ammonium sulphate fractionation and DEAE cellulose chromatography. An electrophoretically homogeneous preparation was modified by chemical and enzymatic methods to examine involvement of specific amino acid residues at the polymerisation, the colchicine binding and the nucleotide binding sites. The modification of tubulin by acetylation and trypsinolysis suggests that lysine residues and the conformation of the protein molecule are important at the colchicine binding site.

The association constants of nucleotides with tubulin show that ATP binds tubulin less efficiently than GTP. The fact that acetylation of tubulin does not affect binding constants, indicates that lysine residues may not be involved at the binding sites of these nucleotides. However, the participation of trytophan residues at the nucleotide binding site is evident from fluorescence studies.