PHASE-TRANSITIONS OF ACHOLEPLASMA-LAIDLAWII MEMBRANES - THE INVOLVEMENT OF MG2-ATPASE IN THE C-TRANSITION()

Highly sensitive differential scanning calorimetry has been employed t o study the phase transitions of A. laidlawii membrane. The DSC curves obtained show five distinct transitions between 20 and 80-degrees-C w hich contain a reversible lipid thermotropic transition at about 37-de grees-C and four irreversible denaturation transitions of the membrane proteins occurred at about 44-degrees-C, 52-degrees-C, 62-degrees-C a nd 67-degrees-C, respectively. Total enthalpy of the thermal denaturat ion of membrane proteins is 3.4 +/- 0.5 cal/g. Further study of A. lai dlawii membrane preparations by means of thermal gel analysis and enzy me acitvity measurements at various temperatures provided information that the third peak (C transition) of the DSC curve involved primarity with Mg2+-ATPase on A. laidlawii membranes.