D-glucose suppression of tyrosine aminotransferase in rat-hepatoma cells grown in culture.

Abstract

A d‐glucose‐free medium containing excess l‐tyrosine was tested for its capacity to induce tyrosine aminotransferase in rat hepatoma cells (Reuber H‐35). Approximately 2 × 107 cells, previously grown in Dulbecco modified Eagle medium were transferred to a similar medium which lacked d‐glucose and contained excess l‐tyrosine. Between 48 and 72 h later a sharp rise in tyrosine‐aminotransferase activity occurred. Addition of d‐glucose at 48 h completely suppressed this increase while l‐glucose had no effect. Conversely, cultures incubated in media containing excess l‐tyrosine in the presence of normal concentrations of d‐glucose were not induced. After 48 h, however, changing from this medium to one which lacked d‐glucose caused a sharp rise in tyrosine‐aminotransferase activity within the next 24 h. The increase in enzyme activity in the absence of d‐glucose was prevented by actinomycin‐D and cycloheximide. It is unlikely that the absence of an energy‐yielding substrate (d‐glucose) caused enzyme induction since replacement of d‐glucose with 2‐deoxyglucose also suppressed tyrosine aminotransferase. Other compounds such as mannitol, lactose, and N‐acetylglucosamine also suppressed synthesis of this enzyme. The data presented suggest that d‐glucose suppresses synthesis by an action initiated at the cell surface.