Abstract—Lactoperoxidase (LPO) which is an enzyme of the mammalian peroxidase family , is known as an antibacterial enzyme, and it can be used as a biopreservative agent in food, feed specialties, cosmetics and related products. Lead (Pb), a heavy metal with no known physiological function in human body, is considered as one of the most hazards that affect all biological systems through exposure from air, water, and food source. The aim of this project was to study the effect of Pb on the Lpo activity isolated from bovine milk in vitro. Bathwise chromatography on phosphocellulose was used for partial purification of LPO from bovine milk by using a linear gradient of Nacl from 0 to 0.5 M. The purified enzyme had specific activity of 1.1 U/mg protein. LPO activity was determined in the absence and Presence of different concentrations of Lead acetate, and Lineweaver-Burk double reciprocal plot was drawn according to the data obtained. Pb2+ inhibited LPO activity progressively up to 0.8 mM concentrations where about 85% of the enzyme activity was lost. The inhibition was found to be non- competitive with respect to 2, 2´- azion- bis (3-ethylbenez- thiazoline-6- sulfonic acid (ABTS). Glutathione (1.2, 12 mM) or β - mercaptoethanol (1.2 mM) protected the enzyme inhibition, and protection by glutathione was concentration dependent. The data suggest a conformational change in the enzyme due to Pb2+ binding caused enzyme inactivation and sulfhydryl groups on the enzyme molecule probably are involved in the inhibition of the enzyme by Pb²⁺.

Index Terms—Enzyme, Lactoperoxidase, Lead, inhibition, non- competitive

M. Defaie is with the Dept. Biology Science & Research Branch‚ Islamic Azad University, Tehran, Iran (corresponding author to provide phone:; fax:+98+21-88970258; e-mail: m.defaie@yahoo.com).
S.Z.Samsam Sharieat is with the Isfahan University of medical sciences, Iran( corresponding author to provide phone; fax:+98+311-6680011;e-mail: samsam@pharm.mui.ac.ir)
A. Divsalar is with the Department of Biological Sciences, Tarbiat Moallem University, Tehran, Iran( e-mail: divsalar@ibb.ut.ac.ir)

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Cite: M. Defaie, S. Z. Samsam Sharieat, A. Divsalar, "Kinetic Investigation on Lactoperoxidase upon Interaction with Lead ion," International Journal of Environmental Science and Development vol. 1, no. 1, pp. 97-100, 2010.