Lipase fraction from the viscera of grey mullet (Mugil cephalus): Isolation, partial purification and some biochemical characteristics

A lipase was partially purified from the viscera of grey mullet (Mugil cephalus) by ammonium sulfate fractionation followed by simultaneous desalting and concentration by ultrafiltration, and affinity chromatography on cholate-EAH-Sepharose 4B. The partially purified grey mullet lipase (GML) was active within the pH range of 7–10, with an optimum pH of 8.0, and was stable from pH 4 to 10. The enzyme was active within the temperature range of 20–60 °C, and exhibited an optimum temperature for the hydrolysis of p-nitrophenyl palmitate at 50 °C, and was stable between 10 and 50 °C, beyond which it lost activity progressively. Based on the temperature activity data, the activation energy for the hydrolysis of p-NPP was calculated as 1.94 kcal/mol (8.15 kJ/mol). The p-nitrophenyl esters of medium to long chain fatty acid (C10–C16) served as good substrates for the enzyme and hydrolytic activity was enhanced by Mg2+, Mn2+, NaN3, and EDTA, but strongly inhibited by Hg2+, and Cu2+. Lower concentrations (25–10%, v/v) of water-miscible organic solvents (dimethyl sulfoxide, dimethyl formamide, iso-propanol, and methanol) had negligible effect on the activity of the lipase while higher concentrations (≥50%, v/v) completely inhibited enzyme activity. GML was remarkably stable in benzene, toluene, hexane, heptane, and iso-octane and was also activated by these solvents with hexane giving the most activation. Lower concentrations of trihydroxylated bile salts (sodium taurocholate, and sodium cholate) were more effective activators of GML than the dihydroxylated bile salt (sodium deoxycholate).