Is cytochrome aa3 from thermus thermophilus a single subunit oxidase?

A reliable procedure has been developed for the purification of the cytochrome c1aa3 complex from the plasma membrane of T. thermophilus. The ratios heme C:heme A:Fe:C were found to be 1:2:3:2 confirming previous results, however, the molecular weight was found to be ~92,000 rather than the ~200,000 reported earlier [1]. Polyacrylamide gel electrophoresis under strongly denaturing conditions and high performance reverse phase liquid chromatography showed that cytochrome c1aa3 is composed of only two subunits in 1:1 ratio. Both polypeptides have blocked N-termini. The smaller subunit (~33,000) binds heme c and presumably no other metals. The larger subunit (~55,000) is thus thought to contain the elements of cytochrome aa3 and therefore be considered a single subunit cytochrome oxidase.The bacterial cytochrome c1aa3 has been compared with beef heart cytochrome oxidase with a number of techniques including optical, EPR [1], Raman, MCD, and Mossbauer [2] spectroscopies. These experiments establish that the fundamental chemical properties of the redox centers are substantially similar in these two proteins.Cytochrome c552 (from Thermus), horse heart cytochrome c, and tetramethylphenylenediamine greatly stimulate the ascorbate oxidase activity of cytochrome c1aa3. This enhancement is characterized by a `high affinity' component which results in only a small velocity increase and a `low affinity' component which gives a large velocity increase. Very similar behavior has been previously observed with mammalian cytochrome oxidase [3].Preliminary experiments show that vesicularized c1aa3 is capable of proton pumping.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25363/1/0000811.pd