Monoclonal antibodies neutralizing mammalian DNA topoisomerase I activity

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Abstract
Tubulin can be post-translationally modified by the incorporation or the release of a tyrosine residue at the COOH-terminus of the .alpha. subunit. The present study demonstrates that rat muscle soluble preparations contain tubulin carboxypeptidase besides tubulin: tyrosine ligase. The state of tyrosination of tubulin and the activities of both the ligase and the carboxypeptidase were examined in rat muscle during development. The proportionof tyrosinated tubulin with respect to tyrosinable tubulin (tyrosinated plus detyrosinated tubulin) decreased from 83% (new-born rats) to 28% (adult rats) with the corresponding increase in detyrosinated tubulin. The activities of the enzymes decreased continuously and in a near parallel fashion during development. These results indicate that the changes in the tyrosination state of tubulin can not be explained merely by changes in the enzyme activities. We also compared the ability of rat muscle and brain [1rC]tyrosinated tubulin to act as substrate of the carboxypeptidase. Muscle tubulin was found to be a less efficient substrate than brain tubulin.