Purification and properties of flagellar outer doublet tubulin from Naegleria gruberi and a radioimmune assay for tubulin.

Outer doublet tubulin has been purified from flagella of differentiated cells of the amebo-flagellate Naegleria gruberi. The flagellar tubulin is similar to other tubulins in molecular weight (55,000), amino acid composition, electrophoretic mobility, and nucleotide composition. However, the protein contains 2 moles of guanine nucleotide per 55,000 g of protein, twice that usually found in tubulin. A rabbit antiserum against flagellar tub&n was shown to contain antibodies specific for tubulin. Purified tubulin iodinated with lzSI was used in a radioimmune assay to measure levels of flagellar tubulin antigen in cells. The measurements indicate that the antigen increases Xito 55-fold during differentiation of amebae to flagellates.