Cp. Witte et al., THE CHLAMYDOMONAS-REINHARDTII MOCO CARRIER PROTEIN IS MULTIMERIC AND STABILIZES MOLYBDOPTERIN COFACTOR IN A MOLYBDATE CHARGED FORM, FEBS letters, 431(2), 1998, pp. 205-209
In Chlamydomonas reinhardtii,, molybdopterin cofactor (MoCo) able to r
econstitute active nitrate reductase (NR) with apoenzyme from the Neur
ospora 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 b
ound to CP was remarkably protected against inactivation under both ae
robic 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 tungstat
e specifically inhibited MoCoCP activity but had no effect on the acti
vity of free MoCo released from milk xanthine oxidase, MoCoCP did not
charge molybdate unless in the presence of N, crassa extracts. Our dat
a support that MoCoCP stabilizes MoCo in an active form charged with m
olybdate to provide MoCo to apomolybdoenzymes. (C) 1998 Federation of
European Biochemical Societies.