title: Reversible thermal inactivation and conformational states in denaturant guanidinium of a calcium-dependent peroxidase from Euphorbia characias.
abstract: The changes in the heme environment and overall structure occurring during reversible thermal inactivation and in denaturant guanidinium of Euphorbia characias latex peroxidase (ELP) were investigated in the presence and absence of calcium ions. Native active enzyme had an absorption spectrum typical of a quantum-mixed spin ferric heme protein. After 40 min at 60 degrees C ELP was fully inactivated showing the spectroscopic behavior of a pure hexacoordinate low-spin protein. The addition of Ca2+ to the thermally inactivated enzyme restored its native activity and its spectroscopic features, but did not increase the stability of the protein in guanidinium. It is concluded that, in Euphorbia peroxidase, Ca2+ ion play a key role in conferring structural stability to the heme environment and in retaining active site geometry.
authors.affiliation: Department of Applied Sciences in Biosystems, University of Cagliari, I-09042 Monserrato, CA, Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Mura
authors.forename: Silvia
authors.initials: S
authors.lastname: Longu
authors.forename: Alessandra
authors.initials: A
authors.lastname: Padiglia
authors.forename: Andrea C
authors.initials: AC
authors.lastname: Rinaldi
authors.forename: Giovanni
authors.initials: G
authors.lastname: Floris
authors.forename: Rosaria
authors.initials: R
authors.lastname: Medda
mesh_terms: D002118:Calcium / Q000737:chemistry*; D004789:Enzyme Activation; D004795:Enzyme Stability; D028481:Euphorbia / Q000201:enzymology*; D019791:Guanidine / Q000737:chemistry; D006418:Heme / Q000737:chemistry*; D007700:Kinetics; D009195:Peroxidase / Q000737:chemistry* / Q000302:isolation & purification; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification; D011487:Protein Conformation; D011489:Protein Denaturation; D013696:Temperature
chemical_list: D010940:Plant Proteins; D006418:Heme; D009195:Peroxidase; D019791:Guanidine; D002118:Calcium