Studies on L-methioninase Formation by Some Yeast Isolates

Abstract

The greater dependency of cancer cells on L-methionine for growth compared to normal cells indicates that depletion of Lmethionine using L-methioninase is effective for cancer therapy. Accordingly, the exploitation of L-methioninase as a promising enzyme for anticancer therapy necessitates the search for new isolates producing L-methioninase. Therefore, the present study focused on screening of different yeast isolates (locally isolated from soil, marine water or some cheese products) for their ability to produce L-methioninase (the subject of this thesis). Optimization of cultural and nutritional conditions required for maximum enzyme formation by the most promising yeast isolate was studied. Moreover, purification and characterization of L-methioninase from CFE of the selected yeast isolate were investigated. In addition, the antitumor activity of the purified enzyme was evaluated. The results obtained in this study could be summarized as follows: 1- Screening studies showed that out of 50 yeast isolates tested, Isolate No.5 was the most promising isolate which showed the highest L-methioninase formation. SUMMARY 169 2- According to identification and taxonomical studies, isolate No. 5 was identified as Candida tropicalis. 3- Among various treatments used to release the intracellular L-methioninase from yeast cells, treatment of yeast cells with N-butanol proved to be the most efficient method for obtaining maximum yield of the enzyme followed in descending order by grinding with sea sand and freezing and thawing methods. 4- On4- On studying some factors affecting crude L-methioninase activity, it was found that the optimum temperature was at 45°C and the highest enzyme activity was obtained at pH 6.5 using 0.075 M sodium citrate buffer. 5- Results concerning optimization of cultural and nutritional conditions required for maximum L-methioninase