Purification and characterization of two endo-1,4-beta-xylanases from Antarctic krill, Euphausia superba Dana

Two Euphausia superba Dana endo-1.4-beta-xylanases (A, and B), hydrolysing xylan in the same manner as the enzyme classified as EC 3.2.1.8, were isolated and purified. (2) The enzymes were distinguished by their molecular mass and charge, affinities towards the oat xylan (Km of 4.1 and 7.7 mg ml(-1), respectively), values of activation energy in oat xylan hydrolysis (35.5 and 42.5 kJ mol(-1), respectively), as well as the way in which they split the substrate. (3) In vitro they showed the same optimal temperature (37-40 degrees C), optimal pH (5.7-6.0), very low thermostability, and were stabilized and activated by Ca2+ and Mg2+ ions, as well as by some unidentified substances with molecular mass less than 17 kDa, present in crude extracts of krill.