X-RAY STUDIES ON THE BILAYER STRUCTURE OF TRYPSIN-TREATED RAT-BRAIN MYELIN

Trypsin-treated rat brain myelin was subjected to biochemical and X-ra y studies. Untreated myelin gave rise to a pattern of three rings with a fundamental repeat period of 155 Angstrom consisting of two bilayer s per repeat period, whereas myelin treated with trypsin showed a fund amental repeat period of 75 Angstrom with one bilayer per repeat perio d. The integrated raw intensity of the h=4 reflection with respect to the h=2 reflection is 0.38 for untreated myelin. The corresponding val ue reduced to 0.23, 0.18, 0.17 for myelin treated with 5, 10, 40 units of trypsin per mg of myelin, respectively, for 30 min at 30 degrees C . The decrease in relative raw intensity of the higher-order reflectio n relative to the lower-order reflection is suggestive of a disorderin g of the phosphate groups upon trypsin treatment or an increased mosai city of the membrane or a combination of both these effects, However, trypsin treatment does not lead to a complete breakdown of the membran e, The integrated intensity of the h=1 reflection, though weak, is abo ve the measurable threshold for untreated myelin, whereas the correspo nding intensity is below the measurable threshold for trypsin-treated myelin, indicating a possible asymmetric to symmetric transition of th e myelin bilayer structure about its centre after trypsin treatment.