Membrane tubulin

Tubulin has been identified as a membrane component of nerve synaptosomes and myelin, plasma membranes of platelets, thyroid, and tissue culture cells, brain and liver coated vesicles, mitochondria, and in cilia but not flagella of certain molluscs. Membrane tubulin can differ from cytoplasmic forms in isoelectric point, non-polar amino acid substitutions, lack of carboxy-terminal tyrosine, carbohydrate content, and selective ability to reassociate with lipids. This tubulin may function as an attachment site for binding vesicles or plasma membranes to cytoplasmic microtubules, as a source of precursor tubulin at the growing tips of axonemes, or as a component of signal transduction in sensory cilia.