Thermal stability of bovine-brain myelin membrane

Abstract

The thermal behaviour of bovine-brain myelin membrane has been studied by high-sensitivity differential scanning calorimetry, Fourier-transform infrared spectroscopy and thermal gel analysis. Spectroscopic results indicate that protein transitions take place between 60 degrees C and 90 degrees C, while thermal gel analysis has provided the thermal denaturation profiles of myelin proteolipid, DM-20 protein and the Wolfgram Fraction. An irreversible calorimetric transition centred at 80.3 +/- 0.2 degrees C with a specific enthalpy of 4.7 +/- 0.6 J/g of total protein has been assigned to the thermal denaturation of myelin proteolipid and DM-20 protein. The effects of the myelin storage conditions, scan rate, ionic strength and pH on this calorimetric transition have also been investigated. The thermal transition of the proteolipid practically disappears after treatment of the myelin with different amounts of chloroform-methanol 2:1 (v/v), a treatment which is generally used in proteolipid purification. On the other hand, the addition of several detergents to myelin only causes minor modifications to this transition, which then occurs at about 70 degrees C, with a specific enthalpy of between 2.5 and 3.6 J/g of total protein. These results appear to show that detergents preserve the native conformation of the proteolipid far more than do organic solvents. Hence the use of detergents would seem to be the appropriate method for proteolipid purification.

Cooling induces phase separation in membranes derived from isolated CNS myelin

“…Upon reaching physiological temperature, where only the native phase remains present, C p reaches a constant value, indicating the completion of the endothermic transition. This result is consistent with earlier work in similar myelin systems and experimental conditions [ 39 – 41 ]. In contrast, at elevated Ca 2+ concentration a monotonic increase in C p with temperature is observed in the entire temperature range, possibly suggesting an ongoing transition.…”

“…Although the curves display only small C p variations, they are very reproducible. Earlier calorimetry work on PMMs [ 39 , 41 ] show a broad endothermic peak at 20–30°C, which has been ascribed to the enthalpies involved in lipid/protein interactions with myelin basic protein (MBP) or Folch´s proteolipid (PLP). In the present work on PMMs we ascribe the broad maxima in C p to the membrane phase transitions seen by SAXS.…”

Scanning Calorimetry and Fourier-Transform Infrared Studies into the Thermal Stability of Cleaved Bacteriorhodopsin Systems

“…Calorimetry experiments with different populations of intact and cleaved BR provide direct evidence for some intermolecular cooperativity upon denaturation. The denatured samples maintain a large proportion of R helices and structure, a fact which seems to be related to their low denaturation enthalpy as compared to that of water-soluble, globular proteins.Thermodynamic-data analysis and energetic characterization of the thermal stability of membrane proteins (SanchezRuiz & Mateo, 1987;Ruiz-Sanz et al, 1992) as well as that of several globular proteins (Sanchez-Ruiz et al, 1988;Conejero-Lara et al, 1991) cannot be undertaken because of their non-equilibrium, irreversible denaturation (SanchezRuiz, 1992). This irreversibility is usually due to nonequilibrium processes taking place on protein unfolding (Klibanov & Ahern, 1987).…”

“…Thermodynamic-data analysis and energetic characterization of the thermal stability of membrane proteins (Sanchez-Ruiz & Mateo, 1987;Ruiz-Sanz et al, 1992) as well as that of several globular proteins (Sanchez-Ruiz et al, 1988;Conejero-Lara et al, 1991) cannot be undertaken because of their non-equilibrium, irreversible denaturation (Sanchez-Ruiz, 1992). This irreversibility is usually due to nonequilibrium processes taking place on protein unfolding (Klibanov & Ahern, 1987).…”