Lactoperoxidase, heme

The human body contains lactoperoxidase, a product of exocrine secretion into milk, saliva, tears, etc., and peroxidases with specialized functions in saliva, the thyroid, eosinophils,219 and neutrophils.220 The functions are largely protective but the enzymes also participate in biosynthesis. Mammalian peroxidases have heme covalently linked to the proteins, as indicated in Fig. 16-12 220 222a... 

The direct interactions between metals and ONOO- can catalyze modifications. For example, the metals in Cu,Zn SOD and FeEDTA (EDTA = ethyl-enediaminetetraacetic acid) enhance nitration reactions (229). Heme-containing enzymes such as myeloperoxidase (6 x 106A/-1 s-1) and lactoperoxidase (3.3 x 105M-1s-1) also react with ONOO- (230) such that compound II [FeIV(P+)0] is formed. In contrast, horseradish peroxidase (3.2 x 106M-1 s-1) is converted to compound I (FevO) by ONOO-. Floris et al. (230) proposed an interesting mechanism by which compound I is initially produced and then rapidly oxidizes NO-f to N02. In the presence of NO, a number of nitrosation reactions would subsequently be facilitated by subsequent formation of N2O3 (Eq. 32). 

DePillis GD, Ozaki S, Kuo JM et al (1997) Autocatalytic processing of heme by lactoperoxidase produces the native protein-bound prosthetic group. J Biol Chem 272 8857-8860... 

Colas C, Kuo JM, Ortiz de Montellano PR (2002) Asp225 and Glu375 in autocatalytic attachment of the prosthetic heme group of lactoperoxidase. J Biol Chem 277 7191-7200... 

Wojciechowski G, Huang L, Ortiz de Montellano PR (2005) Autocatalytic modification of the prosthetic heme of horseradish but not lactoperoxidase by thiocyanate oxidation products. A role for heme-protein covalent crosslinking. J Am Chem Soc 127 15871-15879... 

Aside from the classical examples of hemoglobin and myoglobin, reaction of ferrous heme iron with O2 in hemeperoxidases has been reported for myeloperoxidase [60], horseradish peroxidase C [62], bovine liver catalase [68], lignin peroxidase [46], and lactoperoxidase [61]. With the exception of lactoperoxidase, the binding of O2 is irreversible and CIII engages in one or more of the decay pathways described below. 

Peroxidases fall into two superfamilies (plant and mammalian) and a third, indistinct group that includes chloroperoxidase (a P450-like hybrid) and di-heme cytochrome c peroxidase from Pseudomonas aeruginosa. The plant peroxidase superfamily contains enzymes of plant, fungal, and bacterial origin [126], Mammalian peroxidases make up the second superfamily, and include lactoperoxidase, myeloperoxidase, and prostaglandin H synthase. Both families have been the focus of numerous excellent reviews, several of which have discussed the differences between the plant and mammalian peroxidases [126-130], Here, recent experimental investigations focused on the plant peroxidases will be discussed. 

Hemoproteins are a broad class of redox-proteins that act as cofactors, e.g. cytochrome c, or as biocatalysts, e.g. peroxidases. Direct ET between peroxidases such as horseradish peroxidase, lactoperoxidase," or chloropcroxidasc"" and electrode surfaces, mainly carbonaceous materials, were extensively studied. The mechanistic aspects related with the immobilized peroxidases on electrode surfaces and their utilization in developing biosensor devices were reviewed in detail. The direct electrical contact of peroxidases with electrodes was attributed to the location of the heme site at the exterior of the protein that yields close contact with the electrode surface even though the biocatalyst is randomly deposited on the electrode. For example, it was reported " that non-oriented randomly deposited horseradish peroxidase on a graphite electrode resulted in 40-50% of the adsorbed biocatalyst in an electrically contacted configuration. For other hemoproteins such as cytochrome c it was found that the surface modification of the electrodes with promoter units such as pyridine units induced the binding of the hemoproteins in an orientation that facilitated direct electron transfer. By this method, the promoter sites induce a binding-ET process-desorption mechanism at the modified electrode. Alternatively, the site-specific covalent attachment of hemoproteins such as cytochrome c resulted in the orientation of the protein on the electrode surfaces and direct ET communication. ... 

T. Kitagawa, S. Hashimoto, J. Teraoka, S. Nakamura, H. Yajima, and T. Hosoya, Distinct heme-substrate interactions of lactoperoxidase probed by resonance Raman spectroscopy difference between animal and plant peroxidases. Biochemistry 22 2788 (1983). 

V. Thanabal and G.N. La Mar, A nuclear Overhauser effect investigation of the molecular and electronic structure of the heme crevice in lactoperoxidase. Biochemistry 28 7038 (1989). 

In search of alternatives to Chloramine-T, Morrison (1980) demonstrated that lactoperoxidase from bovine milk was particularly effective for iodide oxidation and the radioiodination of proteins. The single strand polypeptide lactoperoxidase has a molecular weight of approximately 78 kD. The structure of lactoperoxidase contains a prosthetic heme group which is covalently linked to the protein at the active site of the enzyme. In the presence of minute quantities of hydrogen peroxide, lactoperoxidase oxidizes and binds radioiodide to proteins in the reaction mixture. The pH optimum of iodide oxidation by lactoperoxidase is 4-8.5 with an optimum at pH 5. The reaction is extremely rapid, allowing reaction times of less than 1 min. This provides very mild conditions and denaturation of proteins is low. Yields of up to 85% can be obtained and the method is widely used for labeling proteins and hormones. Lactoperoxidase may itself... 

It can be seen that yeast and the plant peroxidases which all contain ferriprotoporphyrin IX behave similarly with a consistent trend in all results. Lactoperoxidase with a heme group of unknown structure behaves much differently in its ligand binding reactions and metmyoglobin (which also contains ferriprotoporphyrin IX) cannot be fit into any peroxidase pattern. In all cases for the peroxidases it is the electrically neutral (protonated) form of the ligand which reacts (see Appendix). For the yeast and plant peroxidases the results for H2O2, HF and HN3 indicate that a dissociative... 

In lactoperoxidase and verdoperoxidase the hemes are also attached covalently to the protein. No thioether link is present in lactoperoxidase alkaline hydrolysis and HI release mesoporphyrin 160). 

Hemoproteins with One or Several Heme Groups per Molecule. Hemoglobins and catalases contain four atoms of iron per molecule, while cytochrome c and the peroxidases (horse-radish and the lactoperoxidases the molecular weight of the others has not yet been determined) contain one iron atom per molecule. For hemoglobin, this means that the hemes within the same molecule exercise considerable interaction, which is of essential importance for the function of hemoglobin. Whether this is also the case in the catalases is not known. In hemoproteins with one iron atom per molecule (peroxidases and cytochrome c) it is evident that no intra-... 

As can be seen from the Table I (page 266), four peroxidases have been produced in a pure or nearly pure state. Two of them have been crystallized, horse-radish peroxidase and lactoperoxidase these are the only ones that have been submitted to any investigations concerning their heme-linked groups. Most of the work has been carried out with horse-radish peroxidase, which is comparatively easily available and has the great advantage that it can be split reversibly into prosthetic group and protein component (71). 

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