Further studies on the induction of omicron-pyrocatechuic acid carboxylyase in aging cultures of Aspergillus ornatus.

The phenomenon of enzyme induction in aging cultures of Aspergillus ornatus was examined under various conditions of culture and induction. Under standard conditions of culture on buffered-defined medium and 6 h induction with 0.1% tryptophan, the tryptophan-inducible specific activity of the enzyme omicron-pyrocatechuic acid carboxylyase decreased 50% with age while the uninduced level of that enzyme remained constant. Increasing the induction time to 10 h allowed the specific activity of the enzyme from older mats to reach the level of the younger mats, which were not affected by increased exposure time to tryptophan. This effect was also achieved by increasing the concentration of the inducer to 1.0%. The effectual concentration of tryptophan, that body of inducer that actually entered the cell, did not change with age, but the incorporation of labeled tryptophan into de novo protein synthesis was depressed from 23 to 35% in older mats.