The Journal of Cell Biology, Vol 94, 263-270, Copyright © 1982 by The Rockefeller University Press
Equimolar heterodimers in microtubules
RE Stephens
Two equimolar beta chains can be resolved from sea urchin sperm flagellar
and scallop gill ciliary tubulins, and from certain brain tubulins as well,
using the Triton X-100-acid-urea polyacrylamide gel system commonly used
for histone analysis. The beta chains are identified as such from their
mobility on urea-free SDS PAGE, from amino acid composition, and from
tryptic peptide distribution. Scallop beta chains have almost identical
amino acid profiles but they differ by one tryptic peptide. Optimal
conditions for beta chain resolution are very species-dependent, with some
closely related species showing either maximal or no beta chain separation.
In addition, beef brain tubulin on Triton X-100-acid-urea electrophoresis
and scallop gill ciliary tubulin upon isoelectric focusing in the presence
of SDS show two approximately equimolar alpha chains. These data,
indicating equimolar amounts of two potentially different tubulin
heterodimers from a variety of microtubule types, support a model for
microtubule structure wherein protofilaments consist of alternating
heterodimers of two kinds, generating a 16-nm (2-dimer) axial repeat.
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