Enzymic hydrolysis of myelin basic protein and other proteins in central nervous system and lymphoid tissues from normal and demyelinating rats

Abstract

Proteolytic activity of central-nervous-system tissue of the normal rat was examined over the pH range 2-9 with casein, haemoglobin and myelin basic proteii as substrates. With casein as a substrate, brain and spinal cord homnogenates showed very similar activity profiles with increasing pH, with the min peaks of proteolytic activity at pH3-4 and 5-6.When haemoglobin was used, one broad main peak ofactivity fromn pH 3 to 5 was demonstrated. There was no optimum pH, however, for proteolytic activity with myelin basic protein as a substrate, and considerable hydrolysis were observed from pH3.5 up to pH8. Proteolytic activity at the various pH values was compared by using homogentaws of spinal cords from rats with acute expenniental allergic encephalomyelitis and those from rats injected with Freund's adjuvant alone. The profiles ofactivity were similar with peaks at pH 3.5 and 5.5 with casein as a substrate, but the specific activity was significantly higher at most pH values in the spinal-cord homogenates from rats with experimental allergic encephalomyelitis. Sinilarly the spinal.'rd homogenates from these latter rats contained much more proteolyticactivitytoward myelin basic protein throughout the pH range than was present in the control spal cords. Homogenates from lymph nodes of rats with experimental allergic encephalomyelitis and from those of the controls contained two to three times as much proteolytic activity as that of the central-nervous-system tissue and had a different proteolytic actvity profile from that of the central nervous system, with higher activity at the neutral than at acid pH. The results are discussed with regard to

Turnover of myelin proteins in mouse brain in vivo

“…These findings indicate that the protein composition of myelin is governed not only by synthesis but also by breakdown. The role of protein breakdown caused by endogenous or exogenous enzymes in demyelination is of great importance and has often been studied in experimental allergic encephalitis Buletza & Smith, 1976).…”

Cleavage of Myelin Basic Protein by Neutral Protease Activity of Human White Matter and Myelin

“…Besides, no catalytic activity of cathepsin D is recorded above pH 6 at which in addition the enzyme ceases to bind pepstatin A (Barrett, 1977). Additional data characterizing neutral proteases of nervous tissue include a broad pH optimum of rat brain homogenates toward MBP as substrate (Buletza and Smith, 1976). N-Ethylmaleimide proved to be a potent inhibitor of neutral proteolysis when used with preparations of MBP of human delipidated white matter (Kies and Deibler, 1973).…”

“…fined. Cerebral white matter and purified myelin were repeatedly shown to exhibit endogenous neutral protease activity either toward isolated MBP (Buletza and Smith, 1976) or toward MBP of tissue preparations (D'Monte et al, 1971; Serra et al, 1972). Autodigestion of purified myelin at pH 7.6, causing a decrease of its basic protein content by 12% within 5 h at 3TC, was attributed to membrane-bound endopeptidase activity (Marks et al, 1976).…”

Myelin

“…Other protease activities present in increased amounts in the CNS of EAE animals include cathepsin A Marks et al, 1977), cathepsin B (Govindarajan et al, 1974), and neutral protease (Govindarajan et al, 1974;. Buletza and Smith (1976) demonstrated increased proteolytic activity in spinal cords of EAE animals throughout the pH range 2.0-8.0. These enzyme increases coincided with infiltration of inflammatory cells into the CNS and the appearance of clinical symptoms; therefore, it seemed most likely that these cells are the source of proteases .…”