Cloning, expression and characterization of metalloproteinase HypZn from Aspergillus niger

A predicted metalloproteinase gene, HypZn, was cloned from Aspergillus niger CGMCC 3.7193 and expressed in Pichia pastoris GS115, and the physicochemical characteristics of recombinant HypZn were investigated after separation and purification. The results showed that the specific activity of the purified HypZn reached 1859.2 U/mg, and the optimum temperature and pH value of HypZn were 35°C and 7.0, respectively. HypZn remained stable both at 40°C and at pH values between 5.0 and 8.0. The preferred substrate of HypZn was soybean protein isolates, and the Km and Vmax values were 21.5 μmol/mL and 4926.6 μmol/(mL∙min), respectively. HypZn was activated by Co2+ and Zn2+ and inhibited by Cu2+ and Fe2+. The degree of soybean protein isolate hydrolysis reached 14.7%, and the hydrolysates were of uniform molecular weight. HypZn could tolerate 5000 mM NaCl and completely lost its activity after 30 min at 50°C. The enzymological characterizations indicated that HypZn has great application potential in the food industry, especially in fermented food processing.

The isolation and characterization of lipase from Carica papaya latex using zwitterion sodium lauroyl sarcosinate as agent

Most of industrial lipases are derived from microbial sources, following by a wide variety of plants. Among plant lipases, lipase from Carica papaya latex has been the focus of intense and growing research due to low cost, easy acceptance by consumers and its unique characteristics. This enzyme has been successfully applied for lipid modification and synthesis of some organic compounds. However, research for its molecular structure has been limited due to the difficulty to isolate the enzyme from the latex matrix. In this study, we suggested a modified approach using sodium lauroyl sarcosinate to solubilize the latex, then the protein was precipitated by ammonium sulphate. We also carried out the characterization of the lipase obtained from Carica papaya latex. The results showed that freeze-drying the fresh latex could improve significantly lipase activity of latex powder in comparison with sun-drying or oven-drying. The zwitterion sodium lauroyl sarcosinate could solubilize nearly 50% of the latex and the achieved supernatant exhibited great lipase activity. There was no need to use an organic solvent to delipidate the latex prior to solubilization with sodium lauroyl sarcosinate due to possible denaturation of enzymes. The proteins which were fractionally precipitated with 50 - 60%, 60 - 70% and 70 - 80% ammonium sulphate saturation showed lipolytic activity. The fraction from 50 - 60% saturation with the greatest mass was subjected to ion exchange chromatography, SDS electrophoresis and kinetic parameter determination. The results showed the presence of two proteins with molecular mass ranging from 35 kDa to 55 kDa and both presented lipase activity. The Km and Vmax of the lipase fraction from 50 - 60% saturation was 1.12 mM and 1.2 x 10-6 mM.min-1.mL-1 respectively. So, the freeze-drying of papaya latex could help to preserve its lipase activity and the usage of sodium lauroyl sarcosinate could improve the isolation of the lipase from the papaya latex and pave the way for research on the molecular structure of Carica papaya latex lipases.