Specific effects on enzyme activities upon ditution of petroselinum hortense cell cultures into water.

Large increases in the specific activities of phenylalanine ammonia-lyase (EC 4.3.1.5) and p-coumarate:CoA ligase (EC 6.2.1.-) occurred within a few hours after dilution of cultured Petroselinum hortense cells into water. No significant changes in the total amount of extractable protein and in the activities of chalcone isomerase (EC 5.5.1.6) and glutamate dehydrogenase (EC 1.4.1.2) were observed under the same conditions. The time course for the change in phenylalanine ammonia-lyase activity included a lag period of 2–3 h, a peak about 13 h after the onset of induction, and a subsequent period of rapid decline. The inducible amount of enzyme activity was greatly dependent upon the degree of dilution of the cells into water. Simultaneous induction by dilution and irradiation of the cells with white, fluorescent light resulted in an increase in the phenylalanine ammonia-lyase level of activity which exceeded that calculated from the sum of the separately induced levels. Consecutive inductions, first by dilution and then 5 h later by irradiation, each required a lag period of 2–3 h. Actinomycin D or cycloheximide were inhibitors of the induction. While the total protein-synthesizing capacity in vitro was not significantly influenced by the dilution of cells, analysis of the labeled products on polyacrylamide gels demonstrated small but significant changes in the radioactivity profiles. The results are consistent with the hypothesis that dilution of the cells into water reduces the concentration of one or more compounds of cellular origin, thereby stimulating the rate of de novo synthesis of a limited number of proteins.