Thermal and structural behavior of natural cerebroside 3-sulfate in bilayer membranes.

Differential scanning calorimetry (DSC), polarizing microscopy and X-ray diffraction studies have been performed on dry and hydrated natural bovine brain sulfatides. Dry sulfatide fractions exhibit a high temperature transition (delta H = 6.6 kcal/mol sulfatide) at 87.3 degrees C. X-ray diffraction shows this transition to be associated with a hydrocarbon chain order-disorder transformation between two lamellar phases. Hydrated sulfatide dispersions undergo a complex chain order-disorder transition (delta H = 7.5 kcal/mol sulfatide) at 32 degrees C with two peak temperatures at 35 degrees C and 47 degrees C. Structural studies performed on hydrated liquid-crystal sulfatide dispersions at 75 degrees C verify the existence of a bilayer structure over the 16 wt.% to 50 wt.% phosphate buffer (pH = 7.4) range. The interbilayer separation between galactosyl-3-sulfate groups averages 48 A as the multilamellar bilayers swell with the addition of phosphate buffer. The formation of micellar phases is not observed at high water contents. The comparison of the structural characteristics of dry and hydrated sulfatides with structural data for dry and hydrated bovine brain non-sulfated glycolipid (cerebroside) is discussed in molecular terms.