Pseudoperoxidase

In 1938, while studying how the pseudoperoxidase (J4) activity of hemoglobin (Hb)1 varied with the experimental conditions, Polonovski and Jayle (P3) fortuitously discovered the occurrence of a substance identified later as haptoglobin (Hp). They found that serum contained a variable amount of a nondialyzable substance which, under certain conditions, made Hb behave like a true peroxidase. Since the substance... 

Fig. 6.10 Schematic representation of the protein modification approaches applied to four peroxidases (Horseradish, chloroperoxidase, cytochrome c, and C. cinereous peroxidase) and proteins with pseudoperoxidase activity (cytochrome P450, myoglobin, and cytochrome c). The dashed arrows link each specific protein modification with the properties improved...

Streefkerk JG. Inhibition of erythrocyte pseudoperoxidase activity by treatment with hydrogen peroxide following methanol. J Histochem Cytochem. 1972 29 829. 

Low concentrations of calcium ion (1-2 pM) are required for maximal activity of purified 5-LO, but the major role of calcium appears to be that of increasing lipophilicity of 5-LO through a C-2-like domain in order to translocate to the nuclear envelope. ATP has a stimulatory effect on 5-LO at 20 nM and lipid hydroperoxides are important to initiate the 5-LO catalytic cycle since they readily form Fe(III) from inactive 5-LO with Fe(II) by the pseudoperoxidase mechanism. Microsomal membranes as well as phosphatidylcholine vesicles can stimulate purified 5-LO activity since 5-LO performs the oxidation of AA at the interface between the membrane and cytosol in a manner similar to that of cPLAja. Calcium ions increase the association of 5-LO with phosphatidylcholine vesicles that likely recapitulate events within the cell where 5-LO becomes associated with the nuclear membrane which is rich in phosphatidylcholine [25]. At the nuclear membrane AA is thought to be presented by a protein which has been termed 5-lipoxygenase activating protein (FLAP) [24]. In cells, such as the neutrophil and mast cells where 5-LO is found in the cytosol, 5-LO is catalytically active only when bound to a membrane, typically the nuclear membrane. In fact, in some cells 5-LO is found to be constitutively associated with the nuclear membrane, likely a result of a process of cellular activation while 5-LO is found in the alveolar macrophage within the nucleus itself [25]. 

Most enzymes in biological cells function as complex enzyme systems. We have prepared artilicial cells that contain multienzyme systems with cofactor recycling." This approach can convert metabolic wastes such as urea and ammonia into essential amino acids such as leucine, isoleucine, and valine, which are required by the body." We have also prepared artificial cells containing hanoglo-bin with pseudoperoxidase activity and glucose oxidase to ranove bilirubin." " ... 

These tests are extremely sensitive but have the disadvantage of not being entirely specific for blood. Such tests are based on the detection of the pseudoperoxidase activity of hemoglobin. The decomposition of a peroxide liberates oxygen, which oxidizes a reduced leukobase, provoking a color change. 

Pseudoperoxidase Activity of Myoglobin Pigment Catalyzed Formation of Radicals in Meat Systems... 

Figure 1. Transformation between myoglobin species. Bold cycle to the lift Color cycle of meat. Bold cycle to the right Pseudoperoxidase cycle of myoglobin. Dotted pathways Not treated in this text (93,94).

Relatively few reports are given in the literature of pseudoperoxidase activity of myoglobin towards proteins. It has been found that myoglobin is a better catalyst for protein oxidation an the classical enzyme horseradish peroxidase, which is usually more effective than myoglobin towards smaller substrates (67.6S). Disulfide and dityrosine cross links are formed when LDL apolipoprotein B (68), myosin 67,69), and other myofibrillar proteins (70) are oxidized by MbFe(IV>0, as summarized for the tyrosine cross-links in myosin (67) ... 

Although the radicals formed by reaction of reducing compounds with hypervalent myoglobin may be harmless, the pseudoperoxidase activity contributes to the depletion of antioxidants in the system and thereby affects the oxidative status of the meat system. 

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