A heat-stable trypsin from the hepatopancreas of the cuttlefish ( Sepia officinalis): Purification and characterisation

Abstract

Thermostable trypsin from the hepatopancreas of Sepia officinalis was purified by fractionation with ammonium sulphate, Sephadex G-100 gel filtration, DEAE-cellulose an ion-exchange chromatography, Sephadex G-75 gel filtration and Q-Sepharose anion-exchange chromatography, with a 26.7-fold increase in specific activity and 21.8% recovery. The molecular weight of the purified enzyme was estimated to be 24,000 Da by SDS-PAGE and size exclusion chromatography. The purified enzyme showed esterase specific activity on Nα -benzoyl-L-arginine ethyl ester (BAEE) and amidase activity on Nα -benzoyl-DL-arginine- p-nitroanilide (BAPNA). The optimum pH and temperature for the enzyme activity were pH 8.0 and 70 °C, respectively, using BAPNA as a substrate. The enzyme was extremely stable in the pH range 6.0–10.0 and highly stable up to 50 °C after 1 h of incubation. The purified enzyme was inhibited by soybean trypsin inhibitor (SBTI) and phenylmethylsulphonyl fluoride (PMSF), a serine-protease inhibitor. The N-terminal amino acid sequence of the first 12 amino acids of the purified trypsin was IVGGKESSPYNQ. S. officinalis trypsin, which showed high homology with trypsins from marine vertebrates and invertebrates, had a charged Lys residue at position 5 and a Ser residue at position 7, where Tyr and Cys are common in all marine vertebrates and mammalian trypsins. Further, the enzyme had an Asn at position 11, not found in any other trypsins. The trypsin kinetic constants, K m and k cat for BAPNA, were 0.064 mM and 2.32 s −1, respectively, while the catalytic efficiency k cat/ K m was 36.3 s −1 mM −1.