DIFFERENT STABILITY OF POSTTRANSLATIONALLY MODIFIED BRAIN MICROTUBULES ISOLATED FROM COLD-TEMPERATE FISH

Microtubule proteins were isolated by a temperature-dependent assembly -disassembly method from brain tissue of for cold-temperate fish; one fresh water fish (Oncorhynchus mykiss), and three marine fish (Labrus berggylta, Zoarces viviparus and Gadus morhua). The alpha-tubulins fro m all four fish species were acetylated. The alpha-tubulins from the m arine fish were composed of a mixture of tyrosinated and detyrosinated tubulin, while the fresh water fish tubulin only reacted with an anti body against detyrosinated tubulin. The isolated microtubules had a si milar MAP composition. A 400 kD protein and a MAP2-like protein were f ound, but MAP1 was missing. All microtubules disassembled upon cooling to 0 degrees C. In spite of these common characteristics, the assembl y of microtubules from Labrus berggylta was inhibited by colchicine an d calcium, in contrast to the assembly of microtubules from Oncorhynch us mykiss and Zoarces viviparus. For the latter, colchicine was not co mpletely inhibitory even at a concentration as high as 1 mM, and calci um induced the formation of both loosely and densely coiled ribbons. T he effects of calcium and colchicine on microtubules from Oncorhynchus mykiss and Zoarces viviparus were modulated by either fish or cow MAP s, indicating that the effects are due to intrinsic properties of the fish tubulins and not the MAPs. In view of these findings, our results suggest that there is no correlation between colchicine sensitivity, inability of calcium to inhibit microtubule assembly, and acetylation and detyrosination.