Tyrosine Transaminase Induction in Mammalian Cells in Tissue Culture

Enzyme induction is known to occur in mammalian systems. Many in vivo studies have provided suggestive evidence of the phenomenon, and in a few cases true induced synthesis of specific enzymes has been shown. One of the best examples has been the induction of liver gluconeogenic enzymes by steroid hormones. (See reviews by Feigelson and Feigelson, 1964, and Nichol and Rosen, 1964, and references therein.) It has been difficult, however, to probe very deeply into the chemical control mechanisms involved while limited to whole animal or perfused organ experiments. Interpretation of such experiments has had to depend heavily on analogy with work done on microorganisms, since there the cell environment is relatively easily controlled and mutations specifically affecting regulatory function can be obtained readily. Obviously it would be desirable to study mammalian control of enzyme synthesis directly in cell culture, but to date only a few systems in which such...