title: Mechanism of interaction of Pb(II) with milk proteins: a case study of alpha-casein.
abstract: Alpha-casein is the major casein protein fraction from bovine milk and is responsible for binding to many ligands. This paper reports the results on the interaction of Pb(II) with alpha-casein. The interaction studies by spectroscopic titration indicate that Pb(II) has two binding sites with an association constant (ka) of (2.3 +/- 0.2) x 10 (5) M(-1). Raman spectra of the alpha-casein-Pb(II) complex show reduction in the amide I region as well as minor perturbations in the sulfhydryl region of alpha-casein. Stopped-flow studies show that the reaction mechanism of Pb(II) follows a pseudo-first-order reaction with a rate of 25 +/- 6 s(-1). The stopped-flow time-resolved spectra show peaks at 330 and 360 nm, correlating to Pb(II)-thiolate bands in the UV absorption spectra. Modification of cysteines present in alpha-casein does not result in binding of lead, indicating that cysteines could be one of the Pb(II) binding sites.
authors.affiliation: Department of Protein Chemistry and Technology, Central Food Technological Research Institute, Mysore 570020, India.
authors.forename: S
authors.initials: S
authors.lastname: Srinivas
authors.forename: Purnima
authors.initials: P
authors.lastname: Kaul
authors.forename: V
authors.initials: V
authors.lastname: Prakash
mesh_terms: D001665:Binding Sites; D002364:Caseins / Q000737:chemistry*; D003545:Cysteine / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D007854:Lead / Q000737:chemistry*; D008894:Milk Proteins / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
chemical_list: D002364:Caseins; D008894:Milk Proteins; D007854:Lead; D003545:Cysteine