MICROCALORIMETRIC STUDY ON THE PHASE-BEHAVIOR OF S-LAYER COATED LIPOSOMES

Isolated S-layer subunits from Bacillus coagulans E38-66/v1 were recry stallized on positively charged, unilamellar liposomes composed of dip almitoylphosphatidylcholine, cholesterol and hexadecylamine. The therm otropic phase behaviour of S-layer coated and uncoated liposomes was c haracterized by differential scanning microcalorimetry indicating for both preparations a broad transition around 50 degrees C due to the ch ain-melting from a liquid-ordered gel-like to a liquid-ordered fluid p hase as described for phosphatidylcholine/cholesterol mixtures. The sl ightly higher phase transition temperature for the S-layer coated lipo somes was explained by increased intermolecular order. Cross-linking t he S-layer subunits covalently to hexadecylamine with glutaraldehyde i nduced phase separation within the liposomes. Based on deconvolution o f the normalized excess heat capacity functions it was proposed that t he different lipid domains arise from phospholipids representing diffe rent degrees of mobility.