Lactoperoxidase source

Bjorck, L. and Claesson, O. 1979. Xanthine oxidase as a source of hydrogen peroxide for the lactoperoxidase system in milk. J. Dairy Sci. 62, 1211-1215. 

As discussed in the earlier survey (1), a biogenic source of polychlorinated dibenzo-p-dioxins and dibenzofurans is peroxidase-catalyzed transformation of chlorophenols as first reported by Oberg and Rappe (2041-2044). More recent studies confirm these observations (2045-2048). In addition to lactoperoxidase and horseradish peroxidase, human leukocyte myeloperoxidase catalyzes in vitro formation of dioxins and dibenzofurans from chlorophenols (2046, 2047). Formation rates are in the pmol/mol range (Scheme 3.6) demonstrating that a human biosynthesis of dioxins and furans is not only possible but also likely. These observations are reinforced by the reported in vivo (rats) conversion of the pre-dioxin nona-chloro-2-phenoxyphenol to octachlorodibenzo-p-dioxin (OCDD) (2049), and the production of hepta- and octachlorodibenzo-p-dioxin in the feces of cows fed pentachlorophenol-treated wood (Scheme 3.7) (2050, 2051). 

Peroxidases from animal sources which have been studied are thyroid peroxidase, lactoperoxidase, myeloperoxidase and glutathione peroxidase. Lactoperoxidase and... 

Figure 10-16 Deactivation of Lactoperoxidase as a Function of Heating Time. Source From F. Kiermeier and C. Kayser, Heat Inactivation of Lactoperoxidase (in German), Z. Lebensm. Untersuch. Forsch., Vol. 113, 1960.

Chloroperoxidase can be produced in batch culture at concentrations of 280 mg L-1,421 and 20 mg of lactoperoxidase can be isolated from 1 L of bovine milk1261. The sources for these two enzymes, bovine milk and culture broth of Caldariomyces... 

Ascorbyl radical can be measured in a steady-state concentration in fresh milk. Oxidation of ascorbate by lactoperoxidase has been proposed to be the source of this radical, based on the increase in ESR signal upon an increase in the concenfra-tion of HjOjand the decrease in signal upon addition of azide (a lactoperoxidase inhibitor) (8). However, the radical may also stem from autoxidation of ascorbic acid in die presence of transition metals (9). 

Radicals may also be produced enzymatically by the lactoperoxidase system, an antimicrobial system naturally present in milk. Lactoperoxidase (EC 1.11.1.7) catalyzes formation of the antimicrobial agent hypothiocyanite (OSCN ) by oxidation of thiocyanate (SCN ) by HjOj (12). One source of HjOj is the enzyme superoxide dimutase (SOD, EC 1.1S. 1.1), which catalyzes dismutation of to O2... 

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