INCREASED SUSCEPTIBILITY TO DEGRADATION BY TRYPSIN AND SUBTILISIN OF IN-VITRO PEROXIDIZED MYELIN PROTEINS

We examined the possibility that the peroxidative damage to central ne rvous system myelin produced by reactive oxygen species (ROS), could m odify the susceptibility of its proteins to the proteolytic action of proteases such as trypsin and subtilisin. Purified myelin membranes ob tained from adult rat brains were ''in vitro'' peroxidized by two non- enzymatic systems: Fe3+ plus ascorbic acid and CU2+ plus hydrogen pero xide. Myelin proteins were severely affected by peroxidation. There wa s an increase in the amount of carbonyl groups (CO), accompanied by an enhanced susceptibility to degradation by trypsin and subtilisin of m yelin basic proteins (MBP) and of the major proteolipid protein (PLP). The effect upon the degradation of myelin protein is a possible conse quence of the appearance in the structure of myelin proteins of peroxi dative modifications that contribute to the recognition by proteolytic enzymes. This hypothesis is supported by the fact that if peroxidatio n of myelin membranes is done in the presence of EDTA, both CO formati on and increased sensitivity to enzymatic breakdown disappear. These r esults suggest that the appearance of abnormal post-translational modi fications in the myelin membrane produced by peroxidation could consti tute a putative mechanism of modulating the capacity of myelin protein s to be metabolized by proteases.