Unanticipated behaviour of sorbitol towards the stability and activity of stem bromelain: An outlook through biophysical techniques

• Biophysical techniques are used for conformational stability of bromelain (BM).
• The stability of BM is dependent on co-solvent concentration.
• CD and FTIR strongly confirm perturbations in BM secondary structure in polyols.
• Unanticipated behaviour of sorbitol towards the stability and activity of BM.

As far as the increased risk of the diseases attributed to the misfolded/unfolded/aggregated proteins are concerned, one may not deny the importance of the various methods (chemical modifications of enzyme, protein engineering techniques and additives) which maintain the protein in its three dimensional functional native form. Out of these methods, the interest in the additives has been grown rapidly in last few decades. Among these additives, polyols are well known compatible co-solvents for the protein. We have investigated the influences of a series of structurally related polyols (ethylene glycol, glycerol, erythritol, xylitol and sorbitol) on the stability and activity of stem bromelain (BM) by using fluorescence spectroscopy, circular dichroism (CD), UV–vis, Fourier transform infrared (FTIR) spectroscopy and dynamic light scattering (DLS). Our results revealed the increased conformational stability of BM with increase in the size of polyols and the proteolytic activity of BM in reverse order. However, sorbitol was found to be the weakest stabilizer for BM among all polyols whereas BM possessed highest activity in the same. To the best of our knowledge, our results represent first detailed unambiguous proof of unusual effect of sorbitol on the interactions governing stability of BM.

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