Rhizomucor miehei lipase: differential scanning calorimetry and pressure/temperature stability studies in presence of soluble additives

In this paper Rhizomucor miehei lipase stability and activity in the presence of polyhydric alcohols and salts, known to be effective protective agents against protein deactivation, were studied. The polyhydric alcohols used (sorbitol, xylitol, erythritol, glycerol and ethylene glycol) differ in their carbon chain length and their hydroxyl group numbers (from 6 to 2). The chosen salts were chloride and bromide ions (alkali halides) such as NaCl, KCl, KBr, NaBr, LiBr and LiCl. Stability criteria used were residual hydrolytic activity and denaturing temperature obtained by differential scanning calorimetry. The results obtained by these two techniques were in accordance. Polyhydric alcohols have been shown to be more effective than salts. Indeed, the best protective effect at 50 °C, is obtained with sorbitol 4 M (the half-life of the lipase is multiplied by a factor 500), whereas this factor only reaches 148 in the presence of salt (KCl 4 M). The protective effect of polyhydric alcohols against thermal and pressure denaturation increases with their concentration and carbon chain length. In the presence of salts, the protective effect depends on their concentration, nature and the enzyme type.