TYROSINATABLE AND NON-TYROSINATABLE TUBULIN SUBPOPULATIONS IN RAT MUSCLE IN COMPARISON WITH THOSE IN BRAIN

Using immunobinding and enzymatic assays we determined in rat muscle extracts the proportion of tyrosinatable tubulin, that is, tubulin that participates in the tyrosination/detyrosination cycle. We found that in muscle, in contrast with nervous tissue, practically all tubulin molecules are tyrosinatable. In the case of rat brain the non-tyrosinatable tubulin pool accounts for about 50% of the tubulin. In addition, isoelectrofocusing of C-14-tyrosinated tubulin from brain and muscle extracts revealed a different composition in tyrosinatable tubulin isotypes. One of the isotypes, which in muscle accounts for 86% of the C-14-tyrosinated tubulin species, was detyrosinated by the action of tubulin carboxypeptidase faster than the rest of the C-14-tyrosinated tubulin isotypes taken in whole. In the case of brain extract, that isotype accounts for only 16% of the labeled tubulin.