A CO-Binding Hemoprotein Derived from Tetrahymena Pyriformis

A CO-binding hemoprotein was purified from Tetrahymena pyriformis and some of its properties were studied. The hemoprotein possessed protoheme, its molecular weight was about 11,000, and its isoelectric point was at pH 8.2. The oxidized form of the hemoprotein showed the Soret band at 406 nmand had no distinct peaks in the region of a- and AY-bands, while the reduced form showed the peaks at 426, 527 and 560 nm. The hemoprotein reacted with CO resulting in shift of the Soret band from 426 to 420 nm. The CO-compound showed a broad band from 537 to 573 nm. The hemoprotein was not autoxidizable or oxygenated either. It did not show either of the cytochrome oxidase, peroxidase and NADH oxidase activities. It should be carefully determined whether or not cytochrome o is functioning as the terminal oxidase in T. pyriformis, as the CO-binding hemoprotein which does not react with molecular oxygen exists in the organism.