Brain and erythrocyte microtubules from chicken contain different beta-tubulin polypeptides.

Abstract

Tubulin subunits isolated from chicken brain tissue and erythrocytes are distinguisbable as unique biochemical species by electrophoret P, and peptide mapping procedures. 1) The subunits of @-tubulin exhibit major differences in electrophoretic mobility on sodium dodecyl sulfate-polyacrylamide gels that vary according to the pH and ionic strength of the gel.2) The isoelectric points of urea-denatured @ subunits from brain tissue and erythrocytes are pH 5.1 and 5.4, respectively, whereas those of both a subunits are approximately pH 5.2.3)Two-dimensional peptide maps prepared with a-chymotrypsin or VS protease show that a-tubulin peptides are indistinguishable, whereas @-tubulin peptides are very different.Only one-third of the 15 major tyrosine-containing @-tubulin peptides prepared with a-chymotrypsin are common to both @tubulin species.The data indicate that the @-tubulin subunits of brain tissue and erythrocytes are biochemically distinct and may be different gene products.The presence of tubulin variants in brain tissue and erythrocytes may indicate special requirements for microtubule assembly and function in different cell types. Chicken erythrocytes containa circumferential band of microtubules that coils around the periphery of the cell close to the cell membrane.The band of microtubules is thought to generate and maintain the discoid shape that is characteristic of these and many other blood cell types.For discussions of the occurrence, properties, and function of microtubule bundles in blood cells see Behnke (1) and White (2).Recently we isolated microtubule protein from chicken erythrocytes by an in uitro assembly procedure, compared it to microtubule protein from chicken brain, and found major differences in protein composition and assembly properties. 1) Microtubule protein isolated from chicken brain by two cycles of in vitro assembly-disassembly contains 70% tubulin, 15% high molecular weight microtubule-associated proteins, and other trace components including (55,000-70,000 M,) 7 factors.Comparable material from chicken erythrocytes contains >95% tubulin with small amounts of 7 polypeptides, hemoglobin, and trace amounts of spectrin-like polypeptides but no microtubule-associated proteins.2) Assembly of erythrocyte microtubules in uitro at 37 "C is distinguished from chicken brain