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Our previous studies showed that sulfanilamide is a new competitive inhibitor of and can be used in the purification of lactoperoxidase (LPO, EC1.11.1.7) from milk. However, this method has some disadvantages like a lower purification factor. The aim of the present study is to improve the purification process of milk LPO from different sources. For this purpose, 16 commercial sulfanilamide derivatives were selected for inhibition studies to determine the best inhibitor of bovine LPO by calculating kinetic parameters. A cyanogen bromide-activated Sepharose 4B affinity matrix was synthesized by coupling with each competitive inhibitor. Among the inhibitors, 5-amino-2-methylbenzenesulfonamide and 2-chloro-4-sulfamoylaniline were used as ligands for the purification of LPO from bovine, buffalo, cow, and goat milks with 1059.37, 509.09, 232.55, and 161.90, and 453.12-, 151.86-, 869.00-, and 447.57-fold, respectively. Our results show that 5-amino-2-methylbenzenesulfonamide, 2-chloro-4-sulfamoylaniline, and 5-amino-1-naphthalenesulfonamide are the best inhibitors for one-step purification of the enzyme.

Secondary sulfonamides (4a–8h) incorporating acetoxybenzamide, triacetoxybenzamide, hydroxybenzamide, and trihydroxybenzamide and possessing thiazole, pyrimidine, pyridine, isoxazole and thiadiazole groups were synthesized. Lactoperoxidase (LPO, E.C.1.11.1.7), as a natural antibacterial agent, is a peroxidase enzyme secreted from salivary, mammary, and other mucosal glands. In the present study, the in vitro inhibitory effects of some secondary sulfonamide derivatives (4a–8h) were examined against LPO. The obtained results reveal that secondary sulfonamide derivatives (4a–8h) are effective LPO inhibitors. The Ki values of secondary sulfonamide derivatives (4a–8h) were found in the range of 1.096 × 10−3 to 1203.83 µM against LPO. However, the most effective inhibition was found for N-(sulfathiazole)-3,4,5-triacetoxybenzamide (6a), with Ki values of 1.096 × 10−3 ± 0.471 × 10−3 µM as non-competitive inhibition.

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