Studies on the lactoperoxidase system: reaction kinetics and antibacterial activity using two methods for hydrogen peroxide generation

Abstract

Components of the lactoperoxidase system were measured during incubation in Isosensitest broth, with enzymatic (glucose oxidase, GO) or chemical (sodium carbonate peroxyhydrate, SCP) means to generate H2O2. When low levels of thiocyanate (SCN-) were used in the GO system, H2O2 was detected and lactoperoxidase (LP) was inactivated when SCN- was depleted. With 10-fold higher SCN-, LP remained active and H2O2 was not detectable. The oxidation product of the LP reaction, most likely hypothiocyanite, was present in low concentrations. When SCP was used for the immediate generation of H2O2 in a system employing low SCN-, half the LP activity was lost within minutes but thereafter it remained stable. Low concentrations of oxidation product were measured and H2O2 was not detected during the course of the experiment. At high SCN- levels, relatively high concentrations of oxidation product were produced immediately, with H2O2 undetectable. The results suggest that the final product of the LP reaction depends on the method of H2O2 generation and the relative proportions of the substrates. Antibacterial activity of the two LPS was tested against an enterotoxigenic strain of Escherichia coli. Both systems showed bactericidal activity within 4 h incubation at 37 degrees C.

Susceptibility of Helicobacter pylori and its urease activity to the peroxidase-hydrogen peroxide-thiocyanate antimicrobial system

“…The short-lived bactericidal effect of the system on H. pylori is in agreement with previous reports of studies with other species of bacteria, in which H 2 O 2 was introduced only at the initiation of the reaction [34,35]. SCN À was used at a concentration of 0.66 mM throughout this study.…”

Crystal Structure of Lactoperoxidase at 2.4 Å Resolution

“…It catalyzes the inactivation of a wide range of microorganisms. [1][2][3] The other members of the mammalian peroxidase family include eosinophil peroxidase (EPO), thyroid peroxidase (TPO), and myeloperoxidase (MPO). 4,5 LPO, EPO, and MPO contribute to the nonimmune host defense system by oxidizing halide and pseudohalide ions to produce potent antimicrobial agents.…”

Antimicrobial effect of the lactoperoxidase system in milk activated by immobilized enzymes

“…Even though SCN" in the milk sample used was sufficient to achieve good LPS antimicrobial activity, a higher concentration of SCN" can protect the immobilized enzymes. For instance, Dionysius et al (1992) reported that H 2 O 2 was not detectable in presence of excess SCN". According to those authors (Dionysius et al 1992), lactoperoxidase was inactivated by H 2 O 2 when SCN" was depleted.…”