The association of tubulin carboxypeptidase with micro-tubules may be involved in the determination of the tyrosi-nation state of the microtubules, . their proportion of tyrosinated vs. nontyrosinated tubulin. We investigated the role of protein phosphatases in the association of carb-oxypeptidase with microtubules in COS cells. Okadaic acid and other PP1/PP2A inhibitors, when added to culture medium before isolation of the cytoskeletal fraction, pro-duced near depletion of the carboxypeptidase activity asso-ciated with microtubules. .
