FIELD: biotechnology, biochemistry, gene engineering, enzymes. SUBSTANCE: invention proposes a method of isolation of endonuclease restriction Bse 21 I recognizing and cleaving the nucleotide sequence 5'-GCTNAGG-3' that ensures to obtain enzyme no containing impurities of nonspecific nucleases and phosphatases and with minimal amount of protein. The yield of enzyme is 3 000 000 U per 10 g of wetted biomass. Isolation of endonuclease restriction Bse 21 I is carried out at the room temperature and pH = 7.5 by fractionation of cellular homogenate in two-phase system polyethylene glycol/dextran in the presence of NaCl taken in concentration 0.2-0.3 M. Purification of enzyme is carried out by chromatography on phosphocellulose P-11 and hydroxylapatite successively. Method provides to obtain up to 30 000 U of enzyme activity/g of biomass that increases the yield of product and decreases the technological process of isolation to 40 h. EFFECT: improved method of preparing, increased yield of enzyme. 1 dwg, 1 tbl, 5 ex
