Influence of metal ions on structure and catalytic activity of papain.

Sathish, H. A. and Kaul, P. and Prakash, V. (2000) Influence of metal ions on structure and catalytic activity of papain. Indian Journal of Biochemistry and Biophysics, 37 (1). pp. 18-27. ISSN 0301-1208

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Abstract

Papain is an endoprotease belonging to cysteine protease family. The catalytic activity of papain in presence of two different metal ions namely zinc and cadmium has been investigated. Both the metal ions are potent inhibitors of the enzyme activity in a concentration dependent manner. The enzyme loses 50% of its activity at 2 x 10(-4) M of CdCl2 and 4 x 10(-4) M of ZnCl2. It is completely inactivated above 1 x 10(-3) M concentration of either ZnCl2 or CdCl2. Of the two metal ions zinc with a ki value of 5 x 10(-5) M is a more potent inhibitor than cadmium which has a ki value of 8 x 10(-5) M. Both the metal ions have higher affinity for active site than the substrate. At concentrations above 1 x 10(-2) M of metal ions the inhibition is not reversible. Calorimetric studies showed decreased thermal stability of papain upon binding of these metal ions. Far UV circular dichroic spectral data showed only small changes in the beta-structure content upon binding of these metal ions. These data are also supported by decrease in the apparent thermal transition temperature of papain by 5 degrees C upon binding of metal ions indicating destabilization of the papain molecule. The mechanism of both partial and complete inactivation of papain in presence of these two metal ions both at lower and higher concentration has been explained.

Item Type:	Article
Uncontrolled Keywords:	papain, proteolytic enzymme, endoprotease, structure
Subjects:	500 Natural Sciences and Mathematics > 10 Plants 500 Natural Sciences and Mathematics > 04 Chemistry and Allied Sciences > 16 Enzyme Chemistry
Divisions:	Protein Chemistry and Technology
Depositing User:	Food Sci. & Technol. Information Services
Date Deposited:	22 Jul 2011 07:07
Last Modified:	22 Jul 2011 07:07
URI:	http://ir.cftri.res.in/id/eprint/2153

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