The effect of temperature on the galactosyl- and sialyltransferases and on the ultrastructure of Golgi membranes.

The effect of temperature on the activity of galactosyl- and sialyltransferases of rat liver Golgi membranes and the galactosyltransferase of serum has been studied. Arrhenius plots for three enzymes were different. Sharp breaks in the curves, indicative of phase transitions were observed for sialyltransferase (28 degree C) of Golgi and galactosyltransferase (34 degree C) of serum but not for galactosyltransferase of Golgi. The activation energy was greater above the break (above 28 degree C) than below for sialyltransferase of Golgi; The activation energy was lower (above 34 degree C) for galactosyltransferase of serum than below. Electron microscopic freeze replicas showed a patchy distribution of particles which increased as the temperature was raised accompanied by smooth areas. This was interpreted as representing lateral phase separation of the membrane components.