An effect of colchicine on galactosyl- and sialyltransferases of rat liver Golgi membranes.

Colchicine inhibited the activity of the galactosyl- and sialyltransferases of rat liver Golgi membranes. The sialyltransferase was more sensitive to the drug than galactosyltransferase since it was inhibited to a greater extent and at lower concentrations of colchicine than the galactosyltransferase. Two soluble enzymes, i.e. that from rat serum and that isolated from bovine milk, were not inhibited by colchicine. Even with very high concentrations of colchicine a marked stimulation of activity was observed. The data suggest that the inhibition observed in the Golgi membranes is in some way related to the arrangement of the enzymes in the lipid bilayer. In support of this hypothesis, the milk galactosyltransferase became very sensitive to colchicine after incorporation of the enzyme into lipid vesicles. The incorporation of colchicine into Golgi membranes was shown to decrease the order parameter as determined by electron spin resonance which reflects an increased fluidity of the Golgi membranes. A change in fluidity may be responsible for the inhibition of enzyme activity at least in part.