Bovine heart subunit, composition

Analysis of the subunit composition of complex I from bovine heart mitochondria. Mol. Cell Proteomics 2, 117-126. 

Subdivision below the monomer level occurs in the presence of sodium dodecyl sulfate and thiols (mercaptoethanol). The oxidase is thus identified as a multisubunit protein. Both yeast (57, 73) and Neitrospora crassa (74) oxidases were shown to be composed of seven subunits. Bovine heart oxidase, on the other hand, has been reported to have between two (75, 76) and six (57, 76) subunits. The subunits from yeast have molecular weights in the range of I, 40,000 II, 33,000 III, 22,000 IV, 14,000 V, 12,700 VI, 12,700 and VII, 4,600 (57, 77). The situation for bovine heart is less clear but the six subunits are reported to have molecular weights around I, 40,000 II, 25,000 III, 19,000 IV, 14,000 V, 10,000 and VI, 8,000 76). When fewer than six subunits are found, their molecular weights invariably correspond to some of the six reported 75-78). The subunit sizes differ for yeast and bovine heart (57). That the protein compositions differ is also reflected in the failure of antibodies against subunits II and VI of yeast oxidase to cross-react with bovine heart oxidase (75). 

Subunit Composition of Bovine Heart Cytochrome be I Compiex... 

Amino acid sequence analysis and determination of subunit composition are painstaking but these steps are usually necessary before further structural investigations are undertaken. It should not be forgotten that chemical composition and amino acid sequencing provided a foundation for recent structure-function findings in the cytochrome oxidase field. The complete amino acid sequence and a successful prediction of the number of a-helices greatly contributed to the successful and rapid crystallographic analysis of bovine heart cytochrome c oxidase at 2.8 resolution, four years ago (Tsukihara et al., 1995 Tsukihara et al., 1996). 

Carroll, J., I. M. Feamley, R. J. Shannon, J. Hirst, and J. E. Walker. 2003, Analysis of the subunit composition of complex I from bovine heart mitochondria. Mol.Cell. Proteomics 2 117-126. 

Thus it is obvious that also the composition of the B-subunit is crucial for oligomycin sensitivity. The homology between the B-subunits from beef heart and the other three sources is (2) E. coli 71.8%, tobacco chloroplast 69.0%, and R. rubrum 76.2%. Both the 6- and the B-subunit of R. rubrum thus show stronger homology with the same subunits from bovine heart mitochondria than do the subunits from chloroplasts and E. coli. 

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