[Extracellular protease biosynthesis in Aspergillus candidus in the absence of carbon or sulfur sources]

The absence of carbon, nitrogen and sulfur sources in the medium was shown to be a prerequisite for the production of exocellular proteases by Aspergillus candidus. The biosynthesis of proteases stops as soon as a limiting substrate is added to the medium. The rate of protease biosynthesis noticeably decreases if proline, alanine, glycine, valine, phenylalanine, serine, threonine, aspartic and glutamic acids are added, particularly during the first hours of incubation. Cysteine increases the delay in the onset of protease biosynthesis. Tryptophan, leucine, asparagine and glutamine considerable decrease the rate of exoprotease biosynthesis throughout the experiment. Arginine, histidine, lysine, ornithine and methionine added to the medium without a carbon source almost entirely inhibit the biosynthesis of exoproteases. A sulfur-deficient fungal mycelium synthesizes exoproteases at a high rate in the medium without a sulfur source whereas sulfate, methionine and cysteine suppress the process. Protein, being the only source of carbon, nitrogen or sulfur in the medium, abruptly decreases the rate of exoprotease biosynthesis.