Thermotropic phase transitions in normal human myelin as observed in a sensitive microcalorimeter

Abstract Using a differential heat capacity calorimeter, phase transitions have been observed in normal human central nervous system myelin. Two large endothermic transitions at 33 and 77°C, respectively, and a smaller transition at 61–62°C, were routinely observed. The relatively simple protein composition of myelin has allowed us to assign the lower transition (33°C) to proteolipid-lipid interactions and the higher temperature transition (72°C) to basic protein-lipid interactions. The small transition at 61–62°C was not assigned, but is probably due to lipid. The abolition of the high temperature transition, after extraction of basic protein from myelin, the lack of phase transitions when a total lipid extract or the isolated proteins were studied, enabled us to assign the high temperature transition. Because the only other major protein was the proteolipid fraction, the low temperature transition (33°C) was assigned to proteolipid-protein interaction.