Infra‐red (ATR/FT) spectroscopic study on the conformational structure of the isolated human gastric mucus pretreated with ethanol

In order to investigate the conformational structure of isolated human gastric mucus gel pretreated with or without ethanol, gel samples were determined by attenuated total reflection/Fourier transform-infra-red (ATR/FT-IR) microspectroscopy. The result indicates that the secondary structure-dependent amide I band and the glycoprotein region were significantly different in the gastric mucus gels pretreated with and without 40% ethanol. The structural composition of β-sheet structure (1640-1600 cm -1 ) increased from 38.48 to 55.08% (+ 16.6%) after 6-hour pretreatment with 40% ethanol, but the β-turn structure, (1660-1700 cm -1 ) decreased from 41.38 to 24.29% (-17.05%). The peak area ranging from 1180 to 1000 cm -1, assigned to the glycoprotein region, was also different after pretreatment with ethanol for 6 h. The higher peak area of the carbohydrate band was obtained in the frequency region between 1000 and 1040 cm -1 and 1100 and 1180 cm ' for mucus gel pretreated with 40% ethanol. However, the peak area ranging from 1100 to 1040 cm -1 mainly due to the symmetric phosphate stretching mode of proteins was somewhat lower for the ethanol-pretreated mucus gel than the native mucus gel. This result strongly reveals that ethanol significantly modified the conformational structure of proteins and carbohydrates of gastric mucus gel. We propose that the dehydration and interference of hydrophobic interactions in the isolated mucus gel after pretreatment with ethanol might be responsible for this conformational change.