PURIFICATION AND SEQUENCE OF RAT EXTRACELLULAR-SUPEROXIDE DISMUTASE-BSECRETED BY C(6) GLIOMA

An enzyme which converts radical oxygen, produced by phorbol 12-myrist ate 13-acetate activated neutrophils, into nonluminescent products is secreted by rat C6 glioma. The enzyme was purified from chemically def ined conditioned media and identified as an extracellular superoxide d ismutase (EC-SOD). The purified enzyme is distinct from human EC-SOD C (Hjalmarsson, K., Marklund, S. L., Engstrom, A., and Edlund, T. (1987 ) Proc. Natl. Acad. Sci. U. S. A. 84, 6340-6344) by its elution from h eparin-Sepharose at 300-400 mM NaCl, its pI of 6.1-7.2, and its native M(r) of 85,000 +/- 20,000. The rat EC-SOD is a dimer with a subunit M (r) of 34,000-36,000 and is extensively modified by post-translational processing. Although rat EC-SOD has a high sequence homology with the catalytic center and the polybasic heparin-binding site near the COOH terminus of human EC-SOD C, its NH2-terminal sequence and the sequenc es flanking the heparin-binding site differ substantially. The sequenc e of the isolated rat EC-SOD cDNA fully confirms the data obtained fro m amino acid sequence analysis. The amino acid sequence of the enzyme and its biochemical properties support its identification as the rat E C-SOD B.