Participation of the hydrophobic bond in complex formation between .KAPPA.-casein and .BETA.-lactoglobulin.

Abstract

It is well known that K-casein plays an important role in stabilizing casein micelles,1} and forms a heat-induced complex with /Mactoglobulin which is one of the main components of whey proteins.2)3) This jc-casein-/?lactoglobulin interaction is of considerable importance in determining the heat stability and rennin clottability of milk and some of its products.4'5) It has been suggested

Interaction between .KAPPA.-casein and .BETA.-lactoglobulin: Effect of calcium.

“…1 and 2). However, it should be noted that the A3 is less reactive with K-C as to formation of the K-C/B-Lg A4 complex compared to a spontaneous reaction in the presence of.EGTA.5) The mean HPLCretention time of the A3 complex in the Ca2+ experiments was 9min compared to 9.5min without EGTA and 1 1.5 min with EGTA (20him), indicating changes in the elution pattern perhaps resulting from conformational changes.10) Ca2 + changes the structure of K-C and exposes hydrophobic regions.12) Doi et al 13) reported that in the presence of Ca2+ the mole ratio of K-C to B-Lg had to be increased to decrease the thermal precipitation of B-Lg, and hence Ca2+ interfered with the complex formation between B-Lg and K-C. The K-C/BLg complex is soluble whereas heat-denatured B-Lg is not.…”

Heat-induced Complex Formation betweenκ-Casein and α-Lactalbumin

“…In our previous papers, the interaction be tween K-casein and fJ-Iactoglobulin was examined!) and the effect of the carbohydrate moiety of K-casein 2 ) and the participation of the hydrophobic bond in the complexform,ation 3 ) were described. Wheelock and his co-workers have studied the effects of heat treatment on milk proteins 4 "'6) and suggested the complex formation between K-casein and ex-Iactalbumin.…”

Protein-Protein Interactions

“…59,75 Purkayastha et al 77 believe that thiol-disulphide interchange is involved in the formation of the ~ lactoglobulin-K-casein complex based on the following findings: no complex was formed when alkylated ~-lactoglobulin and unheated K-casein were heated together; a limited complex was formed when heated and recooled ~-lactoglobulin solution was mixed with K-casein solution and only slight complex formation resulted when heated ~-lactoglobulin was alky-lated. The involvement of disulphide-sulphydryl groups is also postulated by Doi et al 78 based on the findings that the 288-nm peak in the difference spectrum is decreased when the ~-lactoglobulin-K-casein complex is reduced by ~-mercaptoethanol. Moreover ~-lactoglobulin and Scarboxymethylated K-casein do not exhibit complex formation when examined by gel filtration.…”

“…Doi et al 78 examined changes in the ultraviolet spectrum when K-casein, ~-lactoglobulin and the mixtures were heated. They interpreted changes occurring during complex formation to be due to a decrease in the polarity surrounding the tyrosine residue.…”

“…The fluorescence emission spectra of ANS bound to (---) heated and (--) unheated proteins. 78 on adsorption shifts in the ultraviolet difference spectra, it appears that the presence of carbohydrate in K-casein is favourable for hydrophobic bonding with 13-lactoglobulin. 81,82 Further investigations indicate the predominant role of hydrophobic interactions in the initial stages prior to covalent bond formation when mixtures of 13-lactoglobulin and K-casein are heated at 70°C at pH 6.8.…”