“Free” Enzymic Activity of Mitochondrial Fractions from Liver Tumours

As first shown by Kielley and Kielley (1951), mitochondria freshly isolated from liver show little adenosinetriphosphatase (ATP-ase) zactivity, but" latent" activity becomes manifest when the preparations are subjected to procedures such as freezing or dilution with a hypotonic medium. Accordingly, it is generally considered that a low level of "free" ATP-ase activity signifies that the mitochondria have been isolated in an essentially intact state. The situation is similar in the case of acid phosphatase (Berthet and Duve, 1951). Homogenates of primary liver tumours, and mitochondrial fractions derived therefrom, have been extensively studied with respect to enzyme levels in comparison with those in normal liver (Allard, 1955). Such studies have not, however, included measurements of "free " activity as distinct from "total" activity. This aspect has now been studied, with the possibilities in mind that tumour mitochondria may have 'impaired integrity in vivo or may be so fragile as to be readily damaged during their isolation. Particular care has been taken to ensure that the "liver tumours" studied included some hepatomas which, unlike mixed tumours, could reasonably be compared with normal liver.