[Amino acid pool dynamics and extracellular protease biosynthesis in Aspergillus candidus]

The biosynthesis of exocellular proteases by Aspergillus candidus is inhibited if a source of energy, carbon and nitrogen is added to the medium lacking one of these elements. The biosynthesis is not entirely inhibited if a sulfur source is added to the medium deficient in sulfur. The dynamics of free amino acid pool was studied under the conditions of deficiency of carbon, nitrogen and sulfur sources. The absence of a carbon or nitrogen source causes a decrease in the overall amino acid pool. The same correlation is true of most individual amino acids, with the exception of valine, tyrosine and phenylalanine (in the absence of a carbon source), or proline and glycine (in the conditions of deficiency of carbon and nitrogen sources). As soon as the limiting source is added to the medium, the amino acid pool rapidly rises. The deficiency of a sulfur source noticeably decreases the level of most amino acids in the cells. The addition of MgSO4 to the medium restores the pool of sulfur-containing amino acids while changes in the concentration of other amino acids remain the same.