title: Characterisation of an acidic peroxidase from papaya (Carica papaya L. cv Tainung No. 2) latex and its application in the determination of micromolar hydrogen peroxide in milk.
abstract: An acidic peroxidase isoform, POD-A, with a molecular mass of 69.4 kDa and an isoelectric point of 3.5 was purified from papaya latex. Using o-phenylenediamine (OPD) as a hydrogen donor (citrate-phosphate as pH buffer), the optimum pH for the function of POD-A was 4.6, and the optimum temperature was 50°C. The peroxidase activity of POD-A toward hydrogen donors was both pH- and concentration-dependent. Under optimal conditions, POD-A catalysed the oxidation of OPD at higher rates than pyrogallol, catechol, quercetin and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). The chemical modification reagents N-bromosuccinimide and sodium azide significantly inhibited POD-A activity. The results of kinetic studies indicated that POD-A followed a ping-pong mechanism and had a K(m) value of 2.8mM for OPD. Using CPC silica-immobilised POD-A for the determination of micromolar H(2)O(2) in milk, the lower limit of determination was 0.1 μM, and the recoveries of added H(2)O(2) were 96-109%.
authors.affiliation: Department of Food and Nutrition, Providence University, No. 200, Chungchi Rd, Shalu, Taichung 433-01, Taiwan, ROC.
authors.forename: Li-Chun
authors.initials: LC
authors.lastname: Chen
authors.forename: Yun-Chin
authors.initials: YC
authors.lastname: Chung
authors.forename: Chen-Tien
authors.initials: CT
authors.lastname: Chang
mesh_terms: D000818:Animals; D029441:Carica / Q000201:enzymology*; D002417:Cattle; D004795:Enzyme Stability; D005506:Food Contamination / Q000032:analysis; D006861:Hydrogen Peroxide / Q000032:analysis*; D007700:Kinetics; D008892:Milk / Q000737:chemistry*; D009195:Peroxidase / Q000737:chemistry* / Q000302:isolation & purification; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification
chemical_list: D010940:Plant Proteins; D006861:Hydrogen Peroxide; D009195:Peroxidase