Abstract
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 tubulin was shown to contain antibodies specific for tubulin. Purified tubulin iodinated with 125I was used in a radioimmune assay to measure levels of flagellar tubulin antigen in cells. The measurements indicate that the antigen increases 35- to 55-fold during differentiation of amebae to flagellates.