Physical and catalytic properties of a peroxidase derived from cytochrome c.

Except for its redox properties, cytochrome c is an inert protein. However, dissociation of the bond between methionine-80 and the heme iron converts the cytochrome into a peroxidase. Dissociation is accomplished by subjecting the cytochrome to various conditions, including proteolysis and hydrogen peroxide (H(2)O(2))-mediated oxidation.

Neurodegeneration and peroxidases.

Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS) are neurodegenerative diseases that affect different parts of the central nervous system. However, a review of the literature indicates that certain biochemical reactions involved in neurodegeneration in these three diseases are quite similar and could be partly identical. This article critically examines the similarities and, based on data from our own and other laboratories, proposes a novel explanation for neurodegeneration in these three diseases.

Role of peroxidases in Parkinson disease: a hypothesis.

Extensive research has been done to elucidate the underlying molecular events causing neurodegenerative diseases such as Parkinson disease, yet the cause and the individual steps in the progression of such diseases are still unknown. Here we advance the hypothesis that, rather than or in addition to inorganic radical molecules, heme-containing peroxidase enzymes may play a major role in the etiology of Parkinson disease. This hypothesis is based on the following considerations: (1) several heme-containing enzymes with peroxidase activity are present in the substantia nigra pars compacta; (2) these peroxidases have the ability to catalyze the oxidation of proteins and lipids; (3) certain heme peroxidases are known to destroy cells in vivo; (4) heme peroxidases have the stability and specificity that could account for the fact that specific molecules and cells are subject to damage in Parkinson disease, rather than a random destruction; (5) heme peroxidase activity could account for certain reactions in connection with parkinsonism that thus far have not been adequately explained; and (6) the participation of a heme peroxidase could explain some recent observations that are inconsistent with the oxyradical theory.

The cytotoxic activity of lactoperoxidase: enhancement and inhibition by neuroactive compounds.

Neuronal death associated with Parkinson's disease is commonly believed to be caused by oxygen- and nitrogen-derived free radical species. Some years ago, however, we showed that peroxidase from the midbrain of dogs is able to kill various cell types, including neuroblastoma cells (M. B.

The structure of heme proteins Compounds I and II: some misconceptions.

Many reactions catalyzed by heme proteins involve an oxidation of the heme to one or two equivalents above the ferric state. Such intermediates are often referred to as Compound II and Compound I, respectively. Several different notations are used in the literature to describe the chemical structures of these compounds, which has led to errors and misinterpretations.

Synergism of dimethoxybenzosemiquinone free radicals and CD4+ T-lymphocytes to suppress Ehrlich ascites tumor.

Numerous natural and synthetic quinone compounds possess significant antitumor properties. Various mechanisms have been proposed to account for these properties, including scission and degradation of tumor cell DNA, intracellular "redox cycling" to cogenerate semiquinone free radicals and reactive oxygen intermediates, and the interaction of semiquinone radicals with tumor cell surface flavoenzymes. However, no evidence has been presented to explain adequately the preferential attack on tumor cells by semiquinone radicals, as opposed to normal cells.

The toxicities of native and modified hemoglobins.

Recent research on the potential use of hemoglobin derivatives as a blood substitute has revealed that the administration of large quantities of free hemoglobin into the circulation results in a variety of toxic side effects. Because it has been well established that hemoglobin, like myoglobin, has considerable pro-oxidant activity, a number of studies have appeared suggesting that the administered hemoglobins may catalyze various oxidative and peroxidative reactions, which in turn, would cause the observed pathologic conditions. This occurs as a result of the in vivo formation of highly oxidized forms of the native and modified hemoglobins.

The cytotoxic activities of human hemoglobin and diaspirin crosslinked hemoglobin.

It is well known that hemoglobin (Hb) possesses many oxidative enzyme activities, including a pseudo-peroxidase activity. It has also been shown by many investigators that various peroxidases in the presence of hydrogen peroxide and a halide ion exert a potent cytotoxic activity toward various mammalian cell types. It has further been observed by various investigators that the administration of relatively large amounts of purified Hb or a Hb derivative to a host animal during resuscitation experiments leads to a number of unrelated types of tissue damage and cell damage in the host.

Probable immune system mediation of the antitumor activity of the 2,6-dimethoxybenzo-p-semiquinone radical.

We recently reported that the antitumor activity of an immobilized oxidase-peroxidase system, which can produce radical species as intermediates, is dependent on the presence of an intact and functioning immune system in the host. A number of recent investigations have indicated that the bioactive form of many quinone-type anticancer agents may be the semiquinone-type radical. To investigate if the antitumor activity of some of the quinone-type anticancer agents may also be dependent on a fully functioning immune system in the host, we used as a simple, well-defined model the 2,6-dimethoxybenzo-p-semiquinone radical.

Antitumor activity of an immobilized peroxidase system against murine Ehrlich ascites is mediated by the immune system.

Earlier studies have shown that a mixture of glucose oxidase and a peroxidase exerts a tumoricidal effect on rats bearing Novikoff hepatomas when the enzyme mixture is injected intraperitoneally. The enzyme mixture was shown to be nontoxic when injected into healthy animals at levels up to 600 times the therapeutic dose. In the present study, we have evaluated the possibility that the host immune defense system may be involved in the antitumor activity of the peroxidase system, using the murine Ehrlich ascites tumor as the target.

Pilot scale production of pyrogen-free human hemoglobin for research.

A pilot scale production facility for the preparation of 20 to 30 liters of stroma-free hemoglobin is described. The system is capable of producing pyrogen-free solutions for research purposes. It is not certified for production of parenteral solutions for human use, but the plan could be implemented to meet standards for such materials.

Endotoxemia and neutrophil activation in vivo.

There is a growing body of data to suggest that marginated granulocytes mediate much of the pulmonary damage observed during endotoxemia. The mechanism(s) by which endotoxemia initiates neutrophil margination and cytotoxicity remain either controversial or unknown. The objectives of this study were 1) to determine the temporal relationship between endotoxin-induced decreases in mean arterial pressure and circulating neutrophils, 2) to monitor neutrophil activation in vivo by measuring myeloperoxidase (MPO) activity in the plasma and lymph, and 3) to assess the interaction between endotoxin and complement in activation of neutrophilic oxidative metabolism in vitro.

The mechanism of peroxidase-mediated cytotoxicity. II. Role of the heme moiety.

Various peroxidases in the presence of hydrogen peroxide and a halide ion have been shown to exert a cytolytic activity against erythrocytes and other cells. However, few studies have been done to elucidate the active site on the enzymes that is responsible for the cytotoxic activity. In addressing this question we found that boiling of horseradish peroxidase only partially abolishes its cytotoxic activity, suggesting that an intact tertiary structure of the protein may not be essential for the cytotoxic activity.

Peroxidase-induced enhancement of chemiluminescence by murine peritoneal macrophages.

A number of substances have been shown to enhance the respiratory burst (RB) of macrophages. Many of these substances are not normally found in vivo. The present study suggests that a group of enzymes characterized as peroxidases have the ability to significantly enhance the RB and concomitant phagocytosis by murine peritoneal macrophages.

The cytotoxic activity of hematoheme: evidence for two different mechanisms.

Hematoheme displays a potent cytolytic activity toward erythrocytes either in the presence of hydrogen peroxide and a halide ion (system I) or in the presence of oxygen and a reducing agent (system II). In system I it resembles the cytotoxic activity of various peroxidases, whereas in system II it resembles the destructive activity of bleomycin and a variety of metal complexes. Both types of reactions presumably involve the generation of active oxygen species, which are responsible for the damaging effects.

Neuromelanogenic and cytotoxic properties of canine brainstem peroxidase.

We have isolated a heme protein from canine midbrains that possesses potent peroxidase activity. This enzyme catalyzes the oxidation of dopamine to neuromelanin in the presence of H2O2. We have further shown that the isolated peroxidase possesses potent cytotoxic activity in the presence of superoxide or H2O2 and Cl-.

The mechanism of peroxidase-mediated cytotoxicity. I. Comparison of horseradish peroxidase and lactoperoxidase.

The kinetics of the cytolytic activity expressed by lactoperoxidase and horseradish peroxidase toward erythrocytes in the presence of H2O2 and iodide have been investigated at physiological pH. The action of both enzymes was found to be very similar with respect to their kinetic mechanisms. Both enzymes showed saturation kinetics at higher enzyme concentrations under conditions where substrate concentrations were not limiting.

Activation of macrophages by peroxidases.

Peritoneal macrophages from C57BL/6 mice were activated in vitro with various peroxidases and their cytotoxic activity toward 3T12 cells was determined. Destruction of 3T12 cells by macrophages stimulated with horseradish peroxidase, lactoperoxidase, and microperoxidase was observed at peroxidase concentrations as low as 9, 1.6, and 200 nM, respectively.

The cytotoxic activity of hematoporphyrin: studies on the possible role of transition metals.

Hematoporphyrin acquires a potent cytolytic activity toward erythrocytes when activated by visible light. Considerable evidence has been obtained suggesting that this toxic activity is mediated by certain active oxygen species, including singlet oxygen and hydroxyl radicals. These active oxygen species have also been proposed as intermediates in the toxic activity of peroxidases, hemin, and a variety of metal complexes.

Observations on the cytolytic activity of lactoperoxidase using a continuous assay.

A turbidometric assay that allows continuous monitoring of the cytolytic activity of toxic agents toward various target cells has been developed. This assay monitors the change in absorbance at 600 nm (due to light scattering) of a suspension of human red blood cells as a function of time. The rate of cell lysis, delta A600/delta t, can be expressed as the number of cells lysed per minute, which facilitates the determination of kinetic constants.