Characterization of an extracellular asparaginase ofRhodosporidium toruloidesCBS14 exhibiting unique physicochemical properties

Abstract

An asparaginase specific for L-asparagine was purified from Rhodosporidium toruloides CBS14 to apparent homogeneity. The enzyme was associated with L-glutaminase activity (Km, 1.43 × 10−3 M for L-asparagine and 6.45 × 10−3 M for L-glutamine). The enzyme was found to be a homodimer with a subunit molecular mass of 87 kDa. Chemical modification of tryptophan residues significantly reduced both L-asparaginase and L-glutaminase activities of the enzyme, which was prevented by the presence of either of the substrates L-asparagine or L-glutamine. The pH and temperature optima for both activities were 6.35 and 37 °C. The enzyme was serologically identical with the asparaginases of some of the other Rhodotorula and Rhodosporidium yeasts but was distinct from the asparaginase of Saccharomyces cerevisiae.Key words: asparaginase, glutaminase, Rhodosporidium toruloides.