Effect of ethanol on the protein secondary structure of the human gastric mucosa, in vitro

The effect of ethanol on the secondary conformational structure of proteins of the human gastric mucosa was investigated by attenuated total reflection/Fourier transform infrared (ATR/FT-IR) spectroscopy. The IR peak intensity and position of each structural component of gastric mucosa was found to change significantly with the ethanol concentration and length of exposure. The peak intensity due to the beta-sheet and/or beta-turn conformational structure in amide I and II bands of gastric mucosa clearly increased after treatment with ethanol. Moreover, the peak at 1635 cm-1 shifted to 1630 cm-1 after treatment with 40% ethanol for 3 h, or 80% ethanol for 1 h, and a distinct shoulder also appeared at 1643 cm-1. This shift occurred more rapidly and was more pronounced after exposure of mucosa to 80% ethanol, compared with the effect of 40% ethanol, but the alpha-helical structure at the amide I and II bands was not influenced by either concentration of ethanol. Ethanol treatment might also transform the secondary structure of amide III in gastric mucosa from an alpha-helix to a mainly random coil with extensive unfolding. The absorption between 1180 and 980 cm-1, which is assigned to glycoprotein structure, was also reduced after treatment with ethanol. This strongly indicates that ethanol influences the conformation of the lipids and proteins of human gastric mucosa, leading to their deformation.