Localization and Characterization of Tubulin-Like Proteins Associated with Brain Mitochondria: The Presence of a Membrane-Specific Isoform

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Abstract
A mitochondrial fraction, purified from pig brain, was found to contain associated polypeptides with the same electrophoretic migration and isoelectric points as the α- and β-tubulin subunits present in brain microtubules. When analyzed by Western blotting these polypeptides reacted specifically with purified tubulin antibodies. The tubulin-like proteins were then visualized in mitochondrial membranes by protein A-gold complexes after the incubation of purified mitochondria with tubulin antibodies. When membrane and microtubule proteins were compared by isoelectric focussing and two-dimensional gel electrophoresis, differences were observed in the patterns of tubulin isoforms. An additional polypeptide, with the electrophoretic migration of β-tubulin but the isoelectric point of α-tubulin, was found to be enriched in the mitochondrial fraction. This peptide had several Staphylococcus aureus V8 protease peptides in common with α-tubulin and may result from a posttranslational modification of that subunit.