Increased Thermostability and Activity of Chemically Modified Bromoperoxidase from the Red Alga Gracilaria tenuistipitata

Jirasak Kongkiattikajorn^a* and Bhinyo Panijpan^b

 
ABSTRACT: Chemical modification of proteins is widely used as a tool for studying localization of individual amino acids, their participation in the maintenance of the native conformation and for their stabilization. Amino groups of bromoperoxidase from the red seaweed Gracilaria tenuistipitata Chang & Xia (collected in Eastern Thailand, at Ban Laem Sok beach in Trad province) were modified with iodoacetamide to change its structure and to increase its hydrophobicity. The effect of the chemical modification on substrate affinity and catalytic activity were studied. Chemical modification of the enzyme improved the specific activity up to 5 times. In addition, the chemical modification slightly increased the solvent concentration at which the enzyme was catalytically active. The thermostabilities of native and modified bromoperoxidase were assayed. The chemical modification of bromoperoxidase increased its thermostability after incubation at 25^oC for 144 h (about 3.3 fold); the modified form retained 20% of its activity after incubation at 45^oC for 60 h. The optimum pH activity is 5.5 for both native and modified forms of the enzyme. The modified enzyme could tolerate a higher temperature than the native enzyme. This biocatalytic behavior could be attributed to the increased hydrophobicity of the enzyme. On the other hand, the chemical modification of the enzyme altered its hydrophobic characteristic and affected the specific activity.

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a School of Bioresources and Technology, King Mongkut’ s University Technology Thonburi, Thailand.
b Department of Biochemistry, Faculty of Science, Mahidol University, Thailand.

* Corresponding author, E-mail: jirasak.kon@kmutt.ac.th