Characterisation of the chick brain high molecular weight multiply phosphorylated microtubule associated protein

A high-molecular-weight microtubule-associated protein from chick brain, which has previously been shown to be phosphorylated in vitro to the extent of 10-12 mol X mol-1, is shown to have the same properties as reported for the microtubule-associated protein MAP2 from calf and porcine brain in terms of its molecular weight, sensitivity to trypsin and alpha-chymotrypsin, the molecular weights of the primary proteolytic degradation products, and the failure of certain of the latter components to bind to assembled microtubules. The primary 260,000-Mr tryptic product can be phosphorylated to at least 4 mol X mol-1, in contrast to an earlier report with calf brain MAP2 which noted a single phosphorylation.