[Methodological approaches to the study of tumor and body tissue metabolism in vitro and in vivo].

The idea is put forward that in vitro measurements of the potential activity even of the key enzymes are not sufficient for correct evaluation of the rate of complex enzymic processes in vivo. The rate of the in vivo formation of final (not intermediate) products from the corresponding precursors is thought to be the most adequate criterion for it. The idea is substantiated by our studies on the glycolysis enzymes and RNA pyrimidine nucleotide synthesis. Such an approach permits gaining in particular, exact information on both features of the RNA synthesis in experimental tumours and mechanisms underlying a successful competition of the tumour and host tissues for RNA precursors. The latter phenomenon is one of manifestations of the tumour capacity to act as a trap for nitrogen.