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The Chlamydomonas reinhardtii MoCo carrier protein is multimeric and stabilizes molybdopterin cofactor in a molybdate charged form
Author(s) -
Witte Claus-Peter,
Igeño M.Isabel,
Mendel Ralf,
Schwarz Günter,
Fernández Emilio
Publication year - 1998
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/s0014-5793(98)00756-x
Subject(s) - neurospora crassa , molybdenum cofactor , chlamydomonas reinhardtii , biochemistry , molybdate , nitrate reductase , isoelectric point , chemistry , cofactor , crassa , biology , enzyme , mutant , organic chemistry , gene
In Chlamydomonas reinhardtii , molybdopterin cofactor (MoCo) able to reconstitute active nitrate reductase (NR) with apoenzyme from the Neurospora crassa mutant nit ‐1 was found mostly bound to a carrier protein (CP). This protein is scarce in the algal free extracts and has been purified 520‐fold. MoCoCP is a protein of 64 kDa with subunits of 16.5 kDa and an isoelectric point of 4.5. In contrast to free MoCo, MoCo bound to CP was remarkably protected against inactivation under both aerobic conditions and basic pH. MocoCP transferred active MoCo to apoNR in vitro without addition of molybdate, though reconstituted activity was 20% higher in the presence of molybdate. Incubation with tungstate specifically inhibited MoCoCP activity but had no effect on the activity of free MoCo released from milk xanthine oxidase. MoCoCP did not charge molybdate unless in the presence of N. crassa extracts. Our data support that MoCoCP stabilizes MoCo in an active form charged with molybdate to provide MoCo to apomolybdoenzymes.