Regulation of phenylalanine ammonia-lyase activity in cell-suspension cultures of Petroselinum hortense. Apparent rates of enzyme synthesis and degradation.

The time courses for induced changes in the phenylalanine ammonia-lyase activity at five different stages during the growth cycle of cell-suspension cultures from parsley (Petroselinum hortense Hoffm.) were investigated. Large increases in the enzyme activity, induced either by irradiation or by dilution of a cell culture into fresh medium, were followed by an expotential decline to the initial low level. The maximum inducible level of specific enzyme activity varied within a range of about six-fold, depending on the mode of induction and the growth stage of the cell culture.