Purification and Partial Characterization of Major Viscous Protein from Yam (Dioscorea opposita Thunb.) Tuber Mucilage tororo

Abstract

Viscous protein was purified from yam (Dioscorea opposita Thunb.) tuber mucilage tororo by Phenyl-Toyopearl 650M, DEAE-Toyopearl 650M, and CM-Toyopearl 650M column chromatographies, and partially characterized. The molecular weight of the purified protein was estimated to be about 200 kDa, by Native-PAGE and Toyopearl HW-55F gel filtration. Moreover, it had identical subunits of molecular weight of about 32 kDa, either without or with 2-mercaptoethanol, respectively. This protein was identified as dioscorin, the major storage proteins in yam species tubers, when comparing the sequence obtained in an automatic Edman sequencer with the database using FASTA WWW System. On the other hand, the purified protein showed carbonic anhydrase activity and the activity was not inhibited by 2,6-pyridinedicarboxylic acid: zinc atoms were absent in the purified protein. The optimum pH in viscosity was about 5.8 and optimum temperature 20–30°C. Heat denaturation of the protein occurred at about 40°C, but the protein retained more than 66 % of the original viscosity at 70°C for 30 min.