PHOSPHORYLATION IN-VIVO OF CHICK BRAIN MICROTUBULE-ASSOCIATED PHOSPHOLIPIDS

Microtubules were prepared by temperature-dependent cycles of assembly /disassembly from chick brain labeled in vivo with P-32(i) and the dis tribution of labeled phospholipids extracted from cold-insoluble and s oluble microtubular protein fractions was analyzed by thin-layer and p aper chromatography. While P-32-labeling was associated with all of th e phospholipids identified after 2-D TLC, it was found that all of the relatively high radioactivity associated with phosphatidylserine (PS) was in fact associated with a minor co-migrating component which was subsequently identified as phosphatidylinositol(PI) by three independe nt separation procedures. It was estimated that the relative specific radioactivity in PI was several-fold higher than that associated with other microtubule-associated phospholipids. Additional experiments, in which the protein components of once-cycled microtubules were fractio nated by gel permeation chromatography, provided evidence that the 36S component containing ring-like tubulin oligomers (36S) appears to be selectively associated with phospholipid components that were specific ally enriched in P-32-PI. The possible significance of these findings is discussed in relation to the effects of phospholipids on microtubul e dynamics and to the function of microtubules in their interactions w ith membranes.