Pyruvate kinase of hepatoma Morris 5123: insensitivity to dietary changes.

At least two types of pyruvate kinase (ATPpyruvate phosphotransferase, EC 2.7.1.40) have been identified in rat liver, which were named type L (liver) and type M (muscle) on the basis of their immunological properties (Tanaka, Harano, Morimura & Mori, 1965). The L-type enzyme is allosterically activated by fructose 1,6-diphosphate (Taylor & Bailey, 1967) and is subject to hormonal and dietary control (Tanaka et al. 1965; Suda, 1967; Tanaka, Harano, Sue & Morimura, 1967); in particular, it decreases during starvation and increases after feeding with fructose (Bailey, Stirpe & Taylor, 1968). The M-type enzyme is only slightly affected by these factors. The nature ofthe pyruvate kinase of tumours has been investigated: the proportions of Land Mtype enzyme in several transplantable hepatomas have been studied by Lo, Farina, Morris & Weinhouse (1968). Taylor, Morris & Weber (1969) reported that pyruvate kinase of the rapidly growing hepatoma 3924-A differs from rat muscle pyruvate kinase, as judged by the stability to inactivation at 25°C, by the electrophoretic mobility and by the sensitivity to various inhibitors (Cu2+, p-chloromercuribenzoate, ATP, alanine). Criss (1969) observed in well and in poorly differentiated rat hepatomas the occurrence of a new pyruvate kinase isoenzyme, whose electrofocusing mobility was different from that of muscle and M-type liver pyruvate kinase. The purpose of the present investigation was to ascertain whether the pyruvate kinase of the hepatoma Morris 5123 underwent modification after dietary changes. The hepatoma Morris 5123 (Morris, Sidransky, Wagner & Dyer, 1960) from a line maintained in this laboratory was transplanted subcutaneously in male rats of the Buffalo strain, fed on the stock