Purification and characterization of κ-carrageenase from the marine bacterium Pseudoalteromonas porphyrae for hydrolysis of κ-carrageenan

A bacterial strain LL1 producing κ-carrageenase was isolated from the decayed seaweed collected from Yellow Sea, China and identified as Pseudoalteromonas porphyrae. The extracellular κ-carrageenase in the supernatant of cell culture of the marine bacterium P. porphyrae LL1 was purified to homogeneity with a 202.6-fold increase in specific κ-carrageenase activity as compared to that in the supernatant by ultrafiltration, gel filtration chromatography, and anion-exchange chromatography. According to the data from sodium dodecyl sulfatepolyacrylamide gel electrophoresis, the molecular mass of the purified enzyme was estimated to be 40.0 kDa. The purified enzyme could actively convert κ-carrageenan into tetrasaccharides, but poorly convert λ-carrageenan. The optimal pH and temperature of the purified enzyme were 8.0 and 55 °C, respectively. The enzyme was significantly stimulated by Mg2+ and Ba2+. The enzyme was inhibited by phenylmethylsulfonyl fluoride (PMSF), iodoacetic acid, EDTA, EGTA and 1,10-phenanthroline. The Km and Vmax values of the purified enzyme for κ-carrageenan were 4.4 mg/ml and 0.1 mg/min ml, respectively. The amino acid sequence (NPQPHIAKPGQTWILQEKRS) of N-terminus of the purified enzyme was identical to that of N-terminus of the deduced protein encoded by the gene encoding κ-carrageenase cloned from the marine bacterium.