L-asparaginase of Thermus thermophilus: Purification, properties and identificaation of essential amino acids for its catalytic activity

L-asparaginase EC 3.5.1.1 was purified to homogeneity from Thermus thermoph ilus. The apparent molecular mass of L-asparaginase by SDS-PAGE was found t o be 33 kDa, whereas by its mobility on Sephacryl S-300 superfine column wa s around 200 kDa, indicating that the enzyme at the native stage acts as he xamer. The purified enzyme showed a single band on acrylamide gel electroph oresis with pI = 6.0. The optimum pH was 9.2 and the Km for L-asparagine wa s 2.8 mM. It is a thermostable enzyme and it follows linear kinetics even a t 77 degreesC. Chemical modification experiments implied the existence of h istidyl, arginyl and a carboxylic residues located at or near active site w hile serine and mainly cysteine seems to be necessary for active form.