Age-related changes associated with the induction of o-pyrocatechuic acid carboxylyase in Aspergillus ornatus

Abstract

Mycelial mats of Aspergillus ornatus grown on cellulose xanthate membranes placed on a defined agar medium showed o-pyrocatechuic acid carboxylase activity which could be induced to over six times its basal level by the addition of 0.1% l-tryptophan to the medium. Exposure of mature mycelial mats to cycloheximide prior to induction indicated that de novo protein synthesis was required for this induction to occur. The effect of age on this enzyme adaptation process was investigated by transferring membranes and mats of variousages from defined medium to fresh defined medium or defined medium plus 0.1% l-tryptophan With increasing mycelial age, the basal enzyme activity level remained relatively unchanged while the level to which the enzyme could be induced dereased significantly. This decrease was linear when plotted against the mean cell age of the mycelium, conforming to a general model of age-depenedent modifications of the enzyme adaptation process proposed by Adelman. Several possible explanations of this phenomenon are discussed.