Irreversible heat denaturation of bovine α-lactalbumin

Abstract

SUMMARYThe irreversible heat denaturation of α-lactalbumin (α-la) in 0·1 M-phosphate, pH 7·0, at 100 °C was studied using polyacrylamide-gel electrophoresis (PAGE). PAGE revealed two groups of bands, one moving faster than native α-la and one slower, in addition to some denatured protein which remained at the origin and some residual native α-la. The faster group had unchanged molecular weight, but an increase in charge, partly due to hydrolysis of glutamine and asparagine residues. The slower group was shown by two-dimensional sodium dodecyl sulphate-PAGE to be oligomers of denatured α-la; formation of the smaller oligomers preceded the larger ones. The oligomers reverted to monomers in the presence of dithiothreitol, showing that they were disulphide-linked aggregates of denatured α-la. Immuno-blots of the gels showed that both fast and slow groups of bands had irreversibly lost most of the antigenicity of the native protein.

Heat-induced aggregation of bovine lactoferrin at neutral pH: Effect of iron saturation

“…Nevertheless, heatinduced changes to Lf may be related to those observed for a-lactalbumin (a-La), a calcium metallo-protein (Hiraoka, Segawa, Kuwajima, Sugai, & Murai, 1980) that also possesses disulphide bridges (4) and no free thiol groups (Vanaman, Brew, & Hill, 1970). Heating a-La above 85 1C induces the formation of disulphide-linked polymers (Chaplin & Lyster, 1986;Hong & Creamer, 2002;McGuffey, Epting, Kelly, & Foegeding, 2005). The a-La protein may undergo intramolecular disulphide bond cleavage upon heating, exposing free thiols that initiate thiol/disulphide interchange reactions resulting in the formation of polymers and larger aggregates (Hong & Creamer, 2002;McGuffey et al, 2005).…”

Interactions of milk proteins during heat and high hydrostatic pressure treatments — A Review

“…Extensive heating (100°C for at least 10 min) in the absence of extra calcium gives rise to disulfide-bonded α-LA dimers, trimers etc. as well as some nonnative monomeric protein (Chaplin & Lyster, 1986).…”

Comprehensive study of acid gelation of heated milk with model protein systems

“…The reaction is second order when heating is performed in sweet whey (Jelen & Rattray, 1995), and is characterised by two endothermic peaks at 80 C and 140 C and two successive stages (Dannenberg & Kessler, 1988b). Denaturation of a-lactalbumin (alac) is reversible after heating at 20-110 C (Ruegg et al, 1977), but prolonged heating (10-30 min) leads to irreversible denaturation and aggregation (Chaplin & Lyster, 1986). The reaction is first order and a denaturation temperature of 65.2 C has been reported in an SMUF (Ruegg et al, 1977;Dannenberg & Kessler, 1988c).…”