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Abstract
The ability of papain to synthesize the tripeptide Gly-Gly-PheNH2 in saline media at 60°C has been studied, choosing nine different alkali halides (KF, NaF, LiF, KCl, NaCl, LiCl, KBr, NaBr and LiBr) at different concentrations as reaction media. First, papain thermostability in these media was analyzed, and non-first order deactivation kinetics were observed. In all cases, the experimental results were fitted to a two-step series-type deactivation model with excellent agreement. Salts can acts as denaturing or protective agents of the enzyme as a function of both their nature and concentration. Secondly, the effect of these salts on synthesis of the tripeptide Gly-Gly-PheNH2 catalysed by papain was also studied. Salts, as water activity-depressing agents, enhanced the enzyme peptide synthesis by kinetic control proportionally to their concentration and salting-out power. Water activity was shown to be a key parameter in both, the enzyme thermal stability and peptide synthesis activity. The overall results allow a classification of ions on the basis of the increase in synthetic activity and the stabilisation power as follows, F- > Cl- > Br; K+ > Na+ > Li+, which was in agreement with the Hofmeister lyotropic series.
