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Different ratios in 20 S proteasomes and regulatory subunit complexes in two isoforms of the 26 S proteasome purified from rabbit skeletal muscle
Author(s) -
Sawada Hitoshi,
Muto Kazuko,
Fujimuro Masahiro,
Akaishi Takahiro,
Sawada Michiko Takagi,
Yokosawa Hideyoshi,
Goldberg Alfred L.
Publication year - 1993
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(93)80731-9
Subject(s) - proteasome , protein subunit , gene isoform , ubiquitin , biochemistry , size exclusion chromatography , biology , skeletal muscle , chemistry , microbiology and biotechnology , enzyme , gene , anatomy
A ubiquitin/ATP‐dependent proteinase complex (26 S proteasome) was highly purified from rabbit skeletal muscle. The purified 26 S proteasome easily dissociated into a 20 S proteasome and a regulatory subunit complex on non‐denaturing PAGE. By using cleavable and non‐cleavable cross‐linkers, it was revealed that the 26 S proteasome exists in two isoforms: one (D complex) consists of the 20 S proteasome and the regulatory subunit complex in the ratio of one to two, while the other (C complex) exists in an equal molar ratio. Molecular masses of the former and the latter isoforms were estimated to be 1,700 kDa and 1,400 kDa, respectively, by gel filtration, and 2,400 kDa and 1,400 kDa, respectively, by Ferguson plot analysis. Furthermore, both isoforms efficiently hydrolyzed Suc‐Leu‐Leu‐Val‐Tyr‐MCA and ubiquitin‐conjugated [ 125 I]lysozyme. These results suggest that the D and C complexes are active proteinase complexes, most probably corresponding to the dumbbell‐like and mushroom‐like (or space capsule‐like) molecules, respectively.