Tyrocidine synthetase belongs to the group of nonribosomal peptide synthetases (NRPS). The product of its activity is antibiotic tyrocidine. Nonribosomal peptide synthetases are large multienzymatic complexes which synthesize peptides independently of the messenger RNA. Their products are called nonribosomal peptides (NRP). Many of them are used as therapeutics in different branches of medicine. In this theses, the biochemical study was performed on the first module of tyrocidine synthetase, tyrocidine synthetase 1 (TycA). Preliminary studies on this protein have shown that serine residue at the position 291 is phosphorylated. In order to further elucidate the influence of phosphorylation on the enzyme activity, three single point TycA protein variants bearing Ser291Glu, Ser291Ala and Ser291Arg substitutions were constructed. The results indicate that the protein variant with Ser291Glu mutation have 8.3 % lower rate of enzyme activity; Ser291Arg variant have caused 33.3 % higher rate of enzyme activity, while the Ser291Ala variant have 91.6 % higher rate of enzyme activity. The obtained results indicate that Ser291 of the TycA protein probably is phosphorylated, because its substitution with the phosphomimicking glutamic acid leads to the lower enzyme activity by only 8.3 %, which is within acceptable experimental limits, while its mutation in positive arginine or neutral alanine leads to the higher rate of enzyme activity.