Purification and properties of rennin-like enzyme from Aspergillus ochraceus.
An active milk-clotting enzyme was purified some 40-fold from culture supernatant of Aspergillus ochraceus. The purification steps included ammonium sulfate precipitation, G-100 Sephadex gel filtration, and ion exchange chromatography, using DEAE Cellulose column. The enzyme exhibited milk-clotting activity and proteolytic behaviour, an optimum at pH 6.0 and in the range of 7--8.5, respectively. The purified enzyme was actively proteolytic against casein, haemoglobin, and bovine serum albumin at pH 8. The milk-clotting activity was greatly enhanced by manganous ions and by increasing concentrations of calcium chloride. Copper, zinc, and ammonium ions were potent inhibitors of the milk-curdling activity of the purified enzyme. Significant inhibition was also noted with sodium chloride at concentrations of 3% or more. Under the specified reaction condition, maximum rate of proteolysis against casein was obtained at 0.4% substrate concentration, whereas the milk-clotting time was linear proportional to dry skim milk concentration in the range of 8 to 24%. The results are discussed in comparison with other microbial milk-clotting enzymes, and limitations of applicability are also presented.
D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D001230:Aspergillus / Q000201:enzymology*; D002122:Calcium Chloride / Q000494:pharmacology; D002417:Cattle; D010450:Endopeptidases / Q000302:isolation & purification / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008892:Milk / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D012965:Sodium Chloride / Q000494:pharmacology; D013379:Substrate Specificity
D011506:Proteins; D012965:Sodium Chloride; D010450:Endopeptidases; D002122:Calcium Chloride; D001205:Ascorbic Acid