immobilized metal affinity; iminodiacetic acid; tris(2-aminoethyl)amine; protein adsorption; interaction
Immobilized metal ion affinity chromatography (IMAC)is now a widely accepted technique for the purification of natural and recombinant therapeutic products and is beginning to find industrial applications. The design,optimization, and scale-up of a chromatographic process using IMAC demands a thorough understanding to be developed regarding the fundamental factors governing the various interactions between immobilized metal ions and proteins. Consequently, there is an immediate need to find out a theory that is able to account for these interactions most efficiently in a qualitative as well as a quantitative manner. In view of this requirement, the interactions of several model proteins (lysozyme, ovalbumin,bovine serum albumin, conalbumin, and wheat germ agglutinin) with metal (Cu(II), Ni(II))-chelated IDA (iminodiacetate) and tris(2-aminoethyl)amine were investigated.The adsorption data were analyzed using four isotherm models, viz., the general affinity interaction theory/Langmuir model, the Freundlich model, the Temkin model, and the Langmuir–Freundlich model,and the sorption parameters were computed. Although the first three models were applicable to some protein IMA–M(II) systems, the Langmuir–Freundlich model appeared to be the most efficient model for explaining the interactions of proteins with IMA–M(II) gels. Also, this model was able to explain cooperativity and binding heterogeneity in quantitative terms. It is envisaged that this analysis would be useful in developing an improved understanding of protein-immobilized metal ion interactions and providing guidelines for designing preparative-scale separations using IMAC.