β1 and β2 are the designations given to two forms of (5-tubulin that have different electrophoretic mobilities on discontinuous polyacrylamide gels in the presence of sodium dodecyl sulfate [Little, M. (1979) FEBS Lett. 108, 283-286], (3, and β2 constitute respectively 75% and 25% of the total β-tubulin in bovine brain. Although β[ appears to be ubiquitous in animals, β2 has so far only been found in the brains of cows, pigs, deer, rats, chicks, and dogfish but not in squid brain. β2 is not found in bovine kidneys, in porcine lungs, or in any nonchordate tubulin that has been examined. When tubulin is reacted with the sulfhydryl-directed reagent N,-N-ethylenebis(iodoacetamide) (EBI), βb but not β2, is converted to a faster moving form, β*. The yield of β2 in this reaction is not altered by the presence of drugs. When [14C]EBI is used as a probe, most of the label is incorporated into β1 rather than β2. Tubulin molecules that have reacted with EBI to form β* are much less likely to polymerize into microtubules than are molecules that have not formed β*. In view of the observation that only βb and not β2, can form β*, it is possible that βt represents a form of tubulin whose assembly may be regulated by a mechanism involving sulfhydryls. In contrast, β2 may represent a form of tubulin whose assembly is regulated by some other mechanism.
ASJC Scopus subject areas