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Activity and stability of kiwifruit actinidine was determined in various conditions of pH, salt, and temperature using N--CBZ-lysine P-nitrophenyl ester as the substrate. Actinidine activity was low below pH 6, and undetectable below pH 3. The enzyme was stable in a pH range of 6.0-8.5. At 4℃ the enzyme was inactive in the presence of greater than 36% vinegar and in 2 M NaCl. Actinidine at 25℃ was unstable in 24% vinegar but stable in up to 3 M NaCl. With regard to freeze-thaw stability, actinidine retained 85% residual activity after being frozen at -20℃ for 3 days. Based on Arrenius and Lineweaver-Burk plots, actinidine became unstable at greater than 45℃ with only 30% residual activity remaining after 6 min. The Km, kcat, and kcat/Km values of actinidine were 56 uM, 67/sec, and 1.2 uM/sec, respectively.