Structural differences between blood-platelet tubulin and other mammalian tubulins

Carboxymethylated pig blood-platelet tubulin subunits have been characterized by comparing their electrophoretic mobilities and two-dimensional tryptic peptide maps with those of tubulin subunits isolated from four other mammalian tissues. These were pig brain, pig lung, pig sperm and bovine kidney. In addition to the major blood-platelet alpha- and beta-tubulin subunits, minor alpha- and beta-components could be resolved on sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The major blood-platelet beta-tubulin, as well as the minor brain beta 2-tubulin subunit, were clearly tissue specific. In both cases, their two-dimensional peptide maps contained unique heavily labelled peptides. Distinct peptide maps were also observed for the major blood-platelet alpha-tubulin subunit as well as for sperm tail alpha-tubulin, both of which were missing peptides (different in each case) that were present in all of the other alpha-tubulin maps. Under our conditions, a protein with a molecular weight of 70,000 and an isoelectric point of pH 6.4 co-purified with blood-platelet microtubules.