title: Effect of metal ions on structure and activity of papain from Carica papaya.
abstract: Papain, a powerful proteolytic enzyme, is an endoprotease belonging to cysteine endopeptidase family. It is used extensively in food processing especially in tenderization of meat. In this study, we have made an attempt to show the structure activity relationship of this enzyme and the role of calcium and magnesium ions in the activity and stability of the enzyme. Results of activation and stabilization of the enzyme by these cations showed concentration dependent effect. The enzymatic activity of papain increases to a maximum of 18% and 24% in presence of calcium and magnesium ions at 1 x 10(-3) M concentration, respectively. Thermal denaturation studies showed that the binding of calcium and magnesium ions bring about change in the thermal stability of papain at various concentrations of these metal ions. Far ultraviolet circular dichroic studies showed no significant change in the alpha-helix and beta-sheet structure of the papain upon binding of these metal ions. The mechanism underlying the structure activity relationship of papain in presence of these metal ions have been discussed here with reference to the ionic radii, ligand binding preference, coordination numbers and the electrostatic forces between the protein molecule and cations present in the microenvironment of the enzyme.
authors.affiliation: Central Food Technological Research Institute, Department of Protein Chemistry and Technology, IND-570013 Mysore, India.
authors.forename: P
authors.initials: P
authors.lastname: Kaul
authors.forename: H A
authors.initials: HA
authors.lastname: Sathish
authors.forename: V
authors.initials: V
authors.lastname: Prakash
mesh_terms: D001665:Binding Sites; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004789:Enzyme Activation; D006358:Hot Temperature; D008024:Ligands; D008274:Magnesium / Q000378:metabolism / Q000494:pharmacology*; D010206:Papain / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D008024:Ligands; D010206:Papain; D008274:Magnesium; D002118:Calcium