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Calcium‐Stimulated Proteolysis in Myelin: Evidence for a Ca 2+ ‐Activated Neutral Proteinase Associated with Purified Myelin of Rat CNS
Author(s) -
Banik Naren L.,
McAlhaney Walter W.,
Hogan Edward L.
Publication year - 1985
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1985.tb04026.x
Subject(s) - egta , myelin , proteolysis , biochemistry , calcium , chemistry , dithiothreitol , myelin basic protein , leupeptin , myelin proteolipid protein , proteolipid protein 1 , enzyme , biology , endocrinology , central nervous system , protease , organic chemistry
Incubation of myelin purified from rat spinal cord with CaCl 2 (1–5 m M ) in 10–50 m M Tris‐HCl buffer at pH 7.6 containing 2 m M dithiothreitol resulted in the loss of both the large and small myelin basic proteins (MBPs), whereas incubation of myelin with Triton X‐100 (0.25–0.5%) and 5 m M EGTA in the absence of calcium produced preferential extensive loss of proteolipid protein (PLP) relative to MBP. Inclusion of CaCl 2 but not EGTA in the medium containing Triton X‐100 enhanced degradation of both PLP and MBPs. The Ca 2+ ‐activated neutral proteinase (CANP) activity is inhibited by EGTA (5 m M ) and partially inhibited by leupeptin and/or E‐64c. CANP is active at pH 5.5–9.0, with the optimum at 7–8. The threshold of Ca 2+ activation is approximately 100 μ M. The 150K neurofilament protein (NFP) was progressively degraded when incubated with purified myelin in the presence of Ca 2+ These results indicate that purified myelin is associated with and/or contains a CANP whose substrates include MBP, PLP, and 150K NFP. The degradation of PLP (trypsin‐resistant) in the presence of detergent suggests either release of enzyme from membrane and/or structural alteration in the protein molecule rendering it accessible to proteolysis. The myelin‐associated CANP may be important not only in the turnover of myelin proteins but also in myelin breakdown in brain diseases.