Binding of Colchicine-3h to Vinblastine- and Vincristine-induced Crystals in Mammalian Tissue Culture Cells

the vinca alkaloids, vinblastine sulfate and vincristine sulfate (Velban and Oncovin, respectively ; Eli Lilly and Co ., Indianapolis, Ind .), cause hypertrophy of the granular endoplasmic reticulum and annulate lamellae in cultured mammalian cells (7), and the accumulation of large proteinaceous cytoplasmic crystals in tissue culture cells (8), in cells of the central nervous system (9), and in platelets (10) . In electron micrographs, longitudinally cut crystals show a substructure of parallel, electron-opaque lines with approximately 280 A periodicity while in cross-sections a honeycomblike arrangement of tubules, 280 A wide, is seen . Association of large arrays of ribosomes and polyribosomes with the crystals has been recently demonstrated (11, 12) . In cells reincubated in fresh medium after the formation of the vinblastineinduced crystals, large masses of 50-80 A filaments are seen instead of the crystals, suggesting that the crystals and the filaments are interconvertible (11) . Precipitation of a colchicine-binding protein (isolated and characterized earlier [13]) from the high-speed supernates of homogenized tissue culture cells and pig brain, and from isolated microtubular protein, by vinblastine has been reported (14, 15) . Precipitation of structural proteins other than the colchicine-binding microtubular proteins by vinblastine has been recently demonstrated (16) . In view of these observations, it is important to consider whether or not the proteins forming the intracellular cytoplasmic crystals are similar to the colchicine-binding microtubular proteins (13) and the proteins precipitated by vinblastine and vincristine from the supernates of the cell homogenates (14, 15) . BRIEF NOTES