Physicochemical properties of free and immobilized tyrosinase from different species of yam (Dioscorea spp)

Abstract

A shortened method of purification and immobilization of tyrosinase from different species of yam (Dioscorea spp) on insoluble supports is described. The enzyme was purified by aqueous two-phase partitioning (ATPS) followed by gel filtration chromatography. The purified enzyme was immobilized on Ca-alginate, polyacrylamide gel or as cross-linked enzyme aggregate (CLEA) to obtain a yield of between 51–64%, 33–46% and 52–65% respectively for all the yam species. The optimum pH obtained for tyrosinase immobilized on polyacrylamide gel and CLEA was equivalent to that of free enzyme (pH 6.5). In contrast, Ca-alginate entrapped tyrosinase exhibited a shift of optimum pH to 7.0. Entrapped Tyrosinase in polyacrylamide gel and Ca-alginate also retained the same optimum temperature as the free enzyme (50 °C). While the optimum temperature of CLEA shifted to 60 °C. When subjected to four repeated use cycles, tyrosinase entrapped in polyacrylamide gel, Ca-alginate and CLEA still retained close to 40, 35 and 45 % of their initial activities respectively after the fourth cycle. The overall result further suggests yam tyrosinase as a promising enzyme for biocatalysis and biotechnological applications.