The trimethylamine N-oxide aldolase (TMAOase) activity from kidney of European hake (Merluccius merluccius) was characterized by using chromatographic and electrophoretic techniques. Soluble TMAOase was obtained using a differential centrifugation protocol with CHAPS and NaCl buffer. Two TMAOase fractions were isolated by ion exchange chromatography using a FPLC system. For this purpose the weak anion exchanger ANX Sepharose 4 Fast Flow (high sub), suited for high molecular mass proteins, was employed. After anion exchange chromatography, fractions were separated by native electrophoresis. One of the fractions eluted at 0.45 M sodium chloride concentration, and had a charge/mass ratio in electrophoresis similar to bovine serum albumin, with a molecular weight of approximately 100 kDa. The second fraction eluted at 0.7 M sodium chloride concentration, and presented a very low electrophoretic mobility due to either a low charge/mass ratio or due to the presence of protein aggregates of different sizes of between 440 and 2,000 kDa. Proteins present in both TMAOase fractions showed acid isoelectric points of between 4.55 and 5.85

The authors wish to thank the European Commission for financially supporting the Research Projects FAIRCT95–1111 and AIR 3-CT94–1921. Author Rey-Mansilla acknowledges Caixanova for granting a research fellowship

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