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Effects of some vitamins on lactoperoxidase enzyme activity.

OBJECTIVE
The present paper investigates the in vitro effect of L-ascorbic acid (vitamin C), menadione sodium bisulfate (vitamin K3), and folic acid on purified lactoperoxidase (LPO).


METHODS
This enzyme was purified from bovine milk by Amberlite CG 50 resin, CM Sephadex C-50 ion-exchange chromatography, and Sephadex G-100 gel filtration chromatography.


RESULTS
Rz (A412/A280) value for the purified LPO was found to be 0.8. Lactoperoxidase was purified 20.45-fold with a yield of 28.8 %. Purity of enzyme was checked by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) method and a single band was observed. All tested vitamins caused inhibition of the enzyme activity and displayed a competitive type of inhibition mechanism. IC(50) values of these three vitamins were 2.03 microM, 0.025 mM, and 0.0925 mM, and the K(i) constants were 0.508+/-0.257 microM, 0.0107+/-0.0044 mM, and 0.0218+/-0.0019 mM respectively.


CONCLUSION
The vitamins discussed here displayed inhibition-type competition with LPO enzyme at varying concentrations. Our study showed that L-ascorbic acid exhibited a much higher inhibitory effect at lower concentrations, so it was evidently a more potent inhibitor than other vitamins tested.