Thus, by comparing the main properties of the novel L-ASNase from T. sibiricus with previously described homologs from other hyperthermophiles, TsA seems to be promising object for further mutagenesis in order to obtain mesophilic analogs, which will have biotechnology application in view of its high L-ASNase activity, glutaminase activity not exceeding 7%, promising chemical and thermal stability and strong cytotoxic activity toward cancer cells. This evidence concerns the gene GLS and cancer.