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[Effect of amino acids as sole nitrogen sources on exoprotease biosynthesis in Aspergillus candidus].

Aspergillus candidus produced an exocellular protease at a high rate in the absence of nitrogen sources. Nineteen amino acids were added separately as sole nitrogen sources to the medium to study their effect on biosynthesis of exoproteases. All the amino acids were found to repress the biosynthesis, arginine, histidine, lysine and ornithine being most effective among them. Repression of the biosynthesis of exoproteases in the presence of amino acids added as sole nitrogen sources is presumed to be accomplished by ammonium ions which are formed in the course of utilization of amino acids. The level of repression is proportional to the concentration of an amino acid in the medium. Amino acids have no effect on the activity of exocellular proteases synthesized by Aspergillus candidus.