EFFECT OF PRESSURE ON THE DEUTERIUM-EXCHANGE REACTION OF ALPHA-LACTALBUMIN AND BETA-LACTOGLOBULIN

The effect of pressure on the deuterium exchange reaction of alpha-lac talbumin (LA) and beta-lactoglobulin (LG) was investigated to determin e the structural change in these proteins induced by elevated pressure . LG, one of the main components of milk whey, has been degraded selec tively from other milk proteins including LA by protease treatment und er high pressure (Hayashi, R., Kawamura, Y. and Kunugi, S. J. Food Sci . 1987; 52: 1107-1108). This was considered to occur because LG lost i ts native structure under high pressure more remarkably than LA. In th e present study, the HID exchange reaction was carried out under high pressure and the resulting structures were analysed by Fourier-transfo rm infra-red (FTIR) and nuclear magnetic resonance (NMR) spectroscopy, after the release of elevated pressure. The wavenumber of amide I ban ds in the FTIR spectrum assigned to alpha-helix and beta-sheet structu res of the proteins, shifted to lower regions as the H/D exchange of p rotons proceeded. The integral band area of the amide proton signal in low-field regions of the NMR spectrum is related to the HID exchange of less stable protons in the protein. H/D exchanges for LA at 200 MPa and LG at 50 MPa were detectable by NMR as a decrease in the amide pr oton signals, but they were detected less unambiguously by FTIR. This apparent difference may be explained by reference to an intermediary u nfolding stage of the protein that is generated under moderately high pressure.