X-ray diffraction studies on the effect of temperature on the structure of myelin in the sciatic nerve of the frog

1. 1. The effects of temperature on the X-ray diffraction patterns of fresh nerve, normal dried nerve, total lipid extract, and emulsified total nerve lipids, have been studied. 2. 2. Maximal changes in diffraction pattern of fresh nerve were noted between 0 ° C and -2 ° C, and between 58 ° C and 61 ° C. The patterns of dried nerve and total lipid extract showed wide variations in the relative intensities of the 43.0 ± 1.0 Å, and 60.0 ± 1.0 Å bands. Except for a slight decrease in spacings, the other bands remained relatively unaffected over most of the range covered (-20 ° C to 200 ° C). Total nerve lipids emulsified in Ringer solution, showed a marked change in diffraction pattern at the freezing point. 3. 3. A comparison of the changes in diffraction patterns of fresh nerve and emulsified total lipid extract, and those of dried nerve and dried total lipid extract, suggests the presence in myelin of a lipid or lipoprotein complex not present in total nerve lipid extract. The changes in the structure of this complex with temperature appear irreversible. The irreversible changes occur within the range of protein denaturation.