Messenger RNA-controlled Increase of Phenylalanine Ammonia-Lyase Activity in Parsley

Abstract

A specific antiserum [rabbits], raised against purified phenylalanine ammonia-lyase [EC 4.3.1.5] from irradiated cell suspension cultures of parsley (Petroselinum hortense Hoffm.), was used to compare the enzyme species induced either by dilution or by irradiation of the cell suspensions, to investigate the effect of dilution on the rate of synthesis of the enzyme protein in vivo, and to analyze the changes in specific activity of polyribosomal mRNA for the enzyme subunits in vitro. The mRNA activity in vitro was measured by translation of the polyribosomal RNA in a rabbit reticulocyte lysate. The results of immunodiffusion assays indicated that dilution and irradiation of the cell suspensions induced immunologically identical molecular species of phenylalanine ammonia-lyase. Dilution resulted in a large but short-term increase in the rate of synthesis of the enzyme. Highest rates of synthesis were reached after 5-6 h, and were followed by a rapid decline. The curves obtained for the changes in the rate of enzyme synthesis, both in vivo and in vitro, coincided with the curve for changes in the rate of appearance of catalytically active enzyme, as calculated from the observed changes in enzyme activity. Possibly the changes in enzyme activity were caused by corresponding changes in the amount of enzyme-specific polyribosomal mRNA. The dilution of cell cultures had no significant effect on the total rate of incorporation of radioactivity into protein in vivo or on the general template activity of the polyribosomal RNA in vitro throughout at least 25 h.