Characterization of chimeric heme-copper respiratory oxidases using subunits I of Escherichia coli cytochrome bo and Halobacterium salinarium cytochrome aa(3)

We constructed chimeric enzymes with the Escherichia coli cytochrome bo and the Halobacterium salinarium cytochrome mg through recombinant DNA techniques and investigated their spectroscopic and biochemical properties. Although most of the chimeras could not retain hemes in the molecule, the chimeric enzyme containing helix VII of subunit I of the H. salinarium cytochrome mg showed the spectral properties similar to those of the native E. coli oxidase, suggesting that both the low-spin heme b and the high-spin heme o are associated with the chimeric subunit I. However, CUB was absent in the chimera. Helix VII of subunit I of the H. salinarium cytochrome aa(3) is 70% similar to the counterpart of the E. coli cytochrome bo and further contains two invariant histidines which serve as the Cu-B ligands. These results indicate that helix VII must be arranged properly relative to helix VI which provides the third CUB ligand. (C) 1995 Academic Press, Inc.