The third tubulin pool

Tubulin normally undergoes a cycle of detyrosination/tyrosination on the ca rboxy terminus of its alpha-subunit and this results in subpopulations of t yrosinated tubulin and detyrosinated tubulin. Brain tubulin preparations al so contain a third major tubulin subpopulation which is non-tyrosinatable. This review describes the purification and the structural characterization of non-tyrosinatable tubulin. This tubulin variant lacks a carboxyterminal glutamyl-tyrosine group on its alpha-subunit (Delta 2-tubulin). Delta 2-tub ulin is generated from detyrosinated tubulin through an irreversible reacti on. Delta 2-tubulin accumulates in neurons and in stable microtubule assemb lies. It also accumulates in some tumor cells due to the frequent loss of t ubulin tyrosine ligase in such cells. Delta 2-tubulin may be a useful marke r of malignancy in human tumors.