The cytochrome contents in ascites hepatomas and some other fast-growing tumor cells of rats and mice were deter mined spectrophotometrically at room and low temperature and comparedwith those in normal liver cells.On a protein

The cytochrome contents in ascites hepatomas and some other fast-growing tumor cells of rats and mice were deter mined spectrophotometrically at room and low temperature and comparedwith those in normal liver cells.On a protein basis, the contents of cytochromes a(+ a3), b, and c1 in the various hepatomas are rather constant, and the levels are about one-half or one-third of those in normal livers. However, the content of cytochrome c is nearly equal to that in normal livers, and a high c/a(+ a3 ) ratio has been observed in tumor cells. On a cell basis, the cytochrome concentrations in a tumor cell are much lower than those in a normal liver cell. In tumor cells,a considerableamountof cytochromeb [and a part of cytochromes c anda(+ a3)] couldnot bereduced immediately after anaerobiosis or by cyanide or sulfide treat ment, indicating that these cytochromes are not linked to the electron transport chain. In normal liver cells all of the cyto chromes, a(+ a3), b, c, and c1 , are linked directly to the elec tron transport chain. No cytochrome b5 or P450 was detected in the hepatomas and other tumor cells used, while hemoproteins 559 and 565 were present in these cells and their contents were nearly equal to those in normal livers.