Open AccessTwo different aa 3 ‐type cytochromes can be purified from the bacterium Bacillus cereus
Author(s) -
GARCIAHORSMAN J. Arturo,
BARQUERA Blanca,
ESCAMILLA Jose E.
Publication year - 1991
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1991.tb16181.x
Subject(s) - bacillus cereus , antiserum , heme , protein subunit , cytochrome , biochemistry , biology , cytochrome c peroxidase , cytochrome c , yeast , hemeprotein , enzyme , chemistry , stereochemistry , microbiology and biotechnology , bacteria , gene , mitochondrion , antigen , genetics
Two aa 3 ‐type cytochromes were purified from membranes of sporulating Bacillus cereus . One of them, an aa 3 complex, was found to be composed of two subunits (51 and 31 kDa), two a hemes and three copper atoms, thus being similar to the cytochrome aa 3 previously purified from vegetative B. cereus [García‐Horsman, J. A., Barquera, B., González‐Halphen, D. & Escamilla, J. E. (1991) Mol. Microbiol. 5 , 197–205]. The second isoform, a caa 3 complex, was expressed in sporulating cells only, and was found to be composed of two subunits (51 and 37 kDa). The 37‐kDa subunit (subunit II) is a heme‐ c ‐containing polypeptide as shown by its peroxidase activity in SDS/PAGE gels and by its spectral features. Both subunits of the caa 3 complex immunologically cross‐reacted with antiserum raised against B. cereus cytochrome aa 3 , suggesting homology between the two enzymes. Also, the heme‐ c ‐containing subunit of the caa 3 complex was reactive with anti‐(bovine cytochrome c ) antiserum, but not with anti‐(bovine cytochrome c 1 ) antiserum. In addition to one heme c and two hemes a , the caa 3 complex contained three copper atoms. Kinetic comparison of aa 3 and caa 3 complexes revealed that the latter is slightly more active ( k = 150 s −1 ) and has a lower affinity to yeast cytochrome c ( K m = 76 μM) and to oxygen ( K m = 2 μM) as compared with cytochrome aa 3 (100 s −1 , 10 μM, and 5 μM, respectively).