Interaction of Lutein to Protein in Aqueous Solution

Abstract

An interaction between protein and carotenoid was investigated. When ethanol solution of lutein was added to aqueous solution of azuki protein, a combined product which might be considered to a complex between protein and lutein was produced in the form of solution or precipitation. In this case lutein was completely combined to protein till the quantitative ratio of lutein to protein was reached to 8.8×10^-3. pH effected to the formation and the precipitation of the complex. At an isoelectric point heterogeneous precipitants were produced, which were composed of both colored complex and colorless subjected protein. Above this pH homogeneous complex was produced, the molecular weight of which was estimated to be 507, 000 by gel filtration and was not varied by the quantities of added lutein. The complex formation was not appreciably effected by the ionic concentration, and the precipitation of complex easily occured at higher ionic concentration than 0.05M.
Nonionic detergents accerated the formation of complexes while anionic detergents inhibited. The complex formation was strongly inhibited by dissociation agents, both urea and guanidine.
Proteins other than Azuki protein, that is, casein, ovalbumin and soy 11S protein, were also similarly combined to lutein to produce complexes.
From these results it was considered that lutein combined to the hydrophobic parts on the protein surface followed by association to produce complex.