The spectral and enzymatic characterization of cytochrome c1 of liver mitochondria.

The presence of cytochrome cl as a part of the respiratory chain was first reported in 1940 by Yakushiji and Okunuki (1). They concluded from visual spectroscopic observations of heart muscle preparations that this hemoprotein mediates the reactions between cytochromes b and c, as well as between cytochromes b and a. The validity of Yakushiji and Okunuki’s work was questioned by Slater (2), who reported that cytochrome cl is merely a mixture of cytochrome c and a denatured hemochromogen. Meanwhile, Keilin and Hartree (3) had developed a valuable technique for observing the absorption bands of hemoproteins when samples of these pigments were cooled to the temperature of liquid air. They observed by this method, in a variety of different cell types, a pigment distinct from cytochromes c and b, which they called cytochrome e. Widmer et al. (4) have since reported a pigment with similar spectral properties in a preparation of a succinate-cytochrome c reductase from heart muscle. Widmer et al. proposed that such a pigment, which they called “cytochrome 554,” functions enzymatically between cytochromes b and c. Keilin and Hartree (5) have extended their studies on cytochrome e and concluded that it is identical to the cytochrome cl first observed by Yakushiji and Okunuki (1) and thus to that of Widmer et al. (4), “cytochrome 554.” Recently Ball and Cooper (6) have published a paper dealing with observations on the function of cytochromes c and cl. Although they did not make direct measurements on the oxidation and reduction of cytochrome cl, they were able to conclude that cytochrome cl cannot function in the place of cytochrome c in the respiratory chain. They also suggested that if cytochrome cl is concerned in electron transport it works in series with cytochrome c rather than in parallel. The suggestion (1, 4-6) that cytochrome cl (or cytochrome 554) may