'Superactivation' of alkaline phosphatase activity by cycloheximide in rat hepatoma cell cultures

We have found that rat hepatoma cells (R-Y121B) retain alkaline phosphatase activity, and that this enzyme activity is increased by cycloheximide. Actinomycin D also increased the enzyme activity. This increase due to actinomycin D was partially inhibited by cycloheximide. The characteristics of alkaline phosphatase of the cells treated or untreated with cycloheximide or actinomycin D were similar to each other; they were heat labile and the enzyme reaction was strongly inhibited by L-homoarginine, but weakly by L-phenylalanine. The increase in alkaline phosphatase activity with cycloheximide has been termed a 'superactivation' of alkaline phosphatase.