Brain myelin proteolipid has been investigated using high-sensitivity differential scanning calorimetry (DSC) under various conditions. Crude proteolipid with a 40% (80330-1/asset/equation/feb20014579386803301-math-si1.gif?v=1&s=90a73ee9cb28b8e143f59532ef6c34966cc3685b)
) content of protein gave rise to a reversible transition, centered at about 60°C. The specific enthalpy of the transition was 50 + 5 J·g−1 with a calorimetric to van't Hoff enthalpy ratio of 5.7 + 0.5. To our knowledge this is the first intrinsic membrane protein in which a reversible thermal transition has been detected and investigated by DSC. Similar experiments were carried out using the recombinants of delipidated proteolipid and the pool of natural membrane lipids; in this case the transition was less enthalpic and showed lower cooperativity. The recombinants with lecithins, however, did not show any transition at 60°C.
