Comparison of the microtubule proteins of neuroblastoma cells, brain, and Chlamydomonas flagella

Chlamydomonas flagella. I. Isolation and electrophoretic analysis of microtubules, matrix, membranes, and mastigonemes

Methods were developed for the isolation of Chlamydomonas flagella and for their fractionation into membrane, mastigoneme, "matrix," and axoneme components. Each component was studied by electron microscopy and acrylamide gel electrophoresis. Purified membranes retained their tripartite ultrastructure and were shown to contain one high molecular weight protein band on electrophoresis in sodium dodecyl sulfate (SDS)-urea gels. Isolated mastigonemes (hairlike structures which extend laterally from the flagellar membrane in situ) were of uniform size and were constructed of ellipsoidal subunits joined end to end. Electrophoretic analysis of mastigonemes indicated that they contained a single glycoprotein of approximately 170,000 daltons The matrix fraction contained a number of proteins (particularly those of the amorphous material surrounding the microtubules), which became solubilized during membrane removal. Isolated axonemes retained the intact "9 + 2" microtubular structure and could be subfractionated by treatment with heat or detergent. Increasing concentrations of detergent solubilized axonemal microtubules in the following order: one of the two central tubules; the remaining central tubule and the outer wall of the B tubule; the remaining portions of the B tubule; the outer wall of the A tubule; the remainder of the A tubule with the exception of a ribbon of three protofilaments. These three protofilaments appeared to be the "partition" between the lumen of the A and B tubule. Electrophoretic analysis of isolated outer doublets of 9 + 2 flagella of wild-type cells and of "9 + 0" flagella of paralyzed mutants indicated that the outer doublets and central tubules were composed of two microtubule proteins (tubulins 1 and 2) Tubulins 1 and 2 were shown to have apparent molecular weights of 56,000 and 53,000 respectively

Chlamydomonas flagella. II. The distribution of tubulins 1 and 2 in the outer doublet microtubules

Quantitative ultrastructural analysis and quantitative gel electrophoresis of preparations of selectively solubilized Chlamydomonas outer doublets indicated that tubulins 1 and 2 were present in both the A tubule and the B tubule, and that only tubulin 1 was present in the three protofilaments which form the wall ("partition") between the lumens of the A and B tubules. The data suggested that the remaining protofilaments of the outer doublet were grouped together in pairs containing the same type of tubulin, pairs containing tubulin 1 alternating with pairs containing tubulin 2. These findings were used to construct models for the arrangement of the two tubulins in the outer doublet. Further analysis by isoelectric focusing resolved tubulins 1 and 2 into at least five bands.

Rat brain microtubule protein: purification and determination of covalently bound phosphate and carbohydrate

Microtubule protein purified from rat brain by published procedures contains nucleic acid and carbohydrate contaminants. Microtubule protein isolated from the soluble fraction of rat brain homogenates by a new procedure contains no covalently bound amino sugars and no more than 0.2% neutral sugar, but does contain covalently bound phosphate. Total phosphate analysis of rat brain microtubule protein indicates the presence of 0.8 mol of phosphate per mol of protein dimer (110,000 g). The presence of covalently bound phosphate has been confirmed by preparation of (32)P-labeled microtubule protein from rat brain slices maintained in tissue culture in the presence of [(32)P]orthophosphate. Furthermore, phosphorylation is specific to the more negatively charged microtubule protein subunit. (32)P-Labeled serine phosphate has been identified after partial acid hydrolysis of labeled microtubule protein.