title: Purification and characterization of a chymosin from Rhizopus microsporus var. rhizopodiformis.
abstract: Purification and characterization of a chymosin from Rhizopus microsporus var. rhizopodiformis were investigated in the present study. A newly isolated R. microsporus var. rhizopodiformis F518 produced a high level of milk-clotting activity (1,001 SU/mL). A chymosin from the fungus was purified 3.66-fold with a recovery yield of 33.2 %. The enzyme appeared as a single protein band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with a molecular mass of 37.0 kDa. It was optimally active at 60 °C and was stable up to 40 °C. The purified enzyme was an acid protease with an optimum pH of 5.2 and retained 80 % of residual activity within pH 2.0-8.0. The inhibition of 96 and 100 % by pepstatin A at 0.01 and 0.02 mM, respectively, revealed that the enzyme is an aspartic protease. Thus, high milk-clotting activity of the chymosin with good stability will strengthen the potential use of the chymosin as a substitute for calf rennet in cheese manufacturing.
authors.affiliation: College of Food Science and Nutritional Engineering, Beijing Key Laboratory of Functional Food from Plant Resources, China Agricultural University, PO Box 294, No.17 Qinghua Donglu, Haidian District, Beijing, 100083, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Sun
authors.forename: Xi-Ping
authors.initials: XP
authors.lastname: Wang
authors.forename: Qiao-Juan
authors.initials: QJ
authors.lastname: Yan
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: Zheng-Qiang
authors.initials: ZQ
authors.lastname: Jiang
mesh_terms: D012085:Chymosin / Q000737:chemistry* / Q000302:isolation & purification*; D004795:Enzyme Stability; D005656:Fungal Proteins / Q000737:chemistry* / Q000302:isolation & purification*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D012233:Rhizopus / Q000201:enzymology*
chemical_list: D005656:Fungal Proteins; D012085:Chymosin