Increased ornithine decarboxylase activity in murine sarcoma virus infected cells

POLYAMINE biosynthesis is one of the earliest events occurring during cellular proliferation^1,2, and the rate at which it proceeds ³ is limited by ornithine decarboxylase (ODC), an enzyme which catalyses the formation of putrescine from ornithine. ODC levels are low, but stable, in resting cells, and a large increase in activity occurs rapidly after the onset of growth^4,5. Elevated ODC levels occur in certain tumour cells, including hepatoma, neuroblastoma and SV40-transformed cells ^3-7. Fast growing hepatomas have higher enzyme levels than slow growing ones⁶. During Rous sarcoma virus (RSV) transformation, elevation of ODC levels precedes morphological change⁸.