[32S Tubulin oligomer. The resistance to factors suppressing the microtubule formation].

The resistance of brain 32S tubulin oligomer to factors suppressing the microtubules formation: colchicine, CaCl2, cooling and the absence of GTP is studied. The content of oligomer in the preparation and the polymerization degree were estimated by means of analytical centrifugation. Colchicine at 25 degrees and at a concentration of 10 muM does not change and at a concentration of 100 muM only slightly decreases the content of oligomer. The oligomer dissociated (but not completely) in 1 mM colchicine. Tubulin polymerization was partly suppressed by 10 muM and completely--by 100 muM colchicine. CaCl2 at 1 and 10 mM concentrations did not destroy the oligomer but inhibited its polymerization even in lesser of these concentrations. The cooling of the incubation medium to 14 degrees C or 4 degrees C completely inhibited the polymerization and did not affect the content of oligomer in the preparations. Tbulin preparations with low amount of exogenous GTP (less than or equal 3.10(-6) M) had a usual oligomer content, whereas GTP is necessary for polymerization at concentrations exceeding 10(-4) M. Thus, the reaction of tubulin oligomerization is relatively resistant to factors preventing the microtubules assembly. This probably means that there are at least two types of intereaction between tubulin molecules: 1) bonds in microtubules which are sensitive to colchicine, Ca2+ and cold, and which are formed only in the presence of nucleosidetriphosphates; 2) bonds in 32S tubulin oligomer which are more stable and do not need in exogenous nucleotides.