Abstract: Changes of the molecular folding of fruit bromelain perturbed by methanol, ethanol and ethylene glycol have been studied by means of measuring the fluorescence spectra, differential UV-ab-sorbed spectra and circular dichroism spectra.The fluorescence intensity of the enzyme increased distinctly with increasing organic solvent concentrations, suggesting that the microenvironments of aromatic amino acids have distinctly changed.The differential UV-absorbed spectra showed that there were two positive peaks at 232 nm and 288 nm, both of them intensified with increasing concentrations of organic solvents.The 232 nm peak is in concordance with the change of the folding of the enzyme molecules, while the 285 nm peak is in concordance with the change of the microenvironments of tyrosine and tryptophan residues.The circular dichroism spectra showed that the natural enzyme has two negative peaks at 208 nm and 225 nm.These negative peaks of the enzyme perturbed by methanol and ethanol intensified obviously, but in the presence of ethylene glycol, the 225 nm peak increased, while the 208 nm peak decreased and red-shifted in position, eventually the peak disappeared completely at a concentration of 50% of ethylene glycol, indicating that the enzyme molecule has extended completely.

Key words: Fruit bromelain, Organic solvents, Perturbation, Changes of conformation and activity of the enzyme