Publisher Summary Catalase exerts a dual function: (1) decomposition of H 2 O 2 to give H 2 O and O 2 (catalytic activity) and (2) oxidation of H donors, for example, methanol, ethanol, formic acid, phenols, with the consumption of 1 mol of peroxide (peroxide activity) The kinetics of catalase does not obey the normal pattern Measurements of enzyme activity at substrate saturation or determination of the K s is therefore impossible In contrast to reactions proceeding at substrate saturation, the enzymic decomposition of H 2 O 2 is a first-order reaction, the rate of which is always proportional to the peroxide concentration present Consequently, to avoid a rapid decrease in the initial rate of the reaction, the assay must be carried out with relatively low concentrations of H 2 O 2 (about 001 M) This chapter discusses the catalytic activity of catalase The method of choice for biological material, however, is ultraviolet (UV) spectrophotometry Titrimetric methods are suitable for comparative studies For large series of measurements, there are either simple screening tests, which give a quick indication of the approximative catalase activity, or automated methods

Catalase in vitro

Studies on the quantitative and qualitative characterization of erythrocyte glutathione peroxidase

The autoxidation of pyrogallol was investigated in the presence of EDTA in the pH range 7.9–10.6.

The rate of autoxidation increases with increasing pH. At pH 7.9 the reaction is inhibited to 99% by superoxide dismutase, indicating an almost total dependence on the participation of the superoxide anion radical, O2·−, in the reaction. Up to pH 9.1 the reaction is still inhibited to over 90% by superoxide dismutase, but at higher alkalinity, O2·− -independent mechanisms rapidly become dominant.

Catalase has no effect on the autoxidation but decreases the oxygen consumption by half, showing that H2O2 is the stable product of oxygen and that H2O2 is not involved in the autoxidation mechanism.

A simple and rapid method for the assay of superoxide dismutase is described, based on the ability of the enzyme to inhibit the autoxidation of pyrogallol.

A plausible explanation is given for the non-competitive part of the inhibition of catechol O-methyltransferase brought about by pyrogallol.

https://febs.onlinelibrary.wiley.com/doi/epdf/10.1111/j.1432-1033.1974.tb03714.x

Involvement of the Superoxide Anion Radical in the Autoxidation of Pyrogallol and a Convenient Assay for Superoxide Dismutase

There is an increasing amount of experimental evidence that oxidative stress is a causal, or at least an ancillary, factor in the neuropathology of several adult neurodegenerative disorders, as well as in stroke, trauma, and seizures. At the same time, excessive or persistent activation of glutamate-gated ion channels may cause neuronal degeneration in these same conditions. Glutamate and related acidic amino acids are thought to be the major excitatory neurotransmitters in brain and may be utilized by 40 percent of the synapses. Thus, two broad mechanisms--oxidative stress and excessive activation of glutamate receptors--are converging and represent sequential as well as interacting processes that provide a final common pathway for cell vulnerability in the brain. The broad distribution in brain of the processes regulating oxidative stress and mediating glutamatergic neurotransmission may explain the wide range of disorders in which both have been implicated. Yet differential expression of components of the processes in particular neuronal systems may account for selective neurodegeneration in certain disorders.

https://science.sciencemag.org/content/sci/262/5134/689.full.pdf

Oxidative stress, glutamate, and neurodegenerative disorders

O2- oxidizes the [4Fe-4S] clusters of dehydratases, such as aconitase, causing-inactivation and release of Fe(II), which may then reduce H2O2 to OH- +OH.. SODs inhibit such HO. production by scavengingO2-, but Cu, ZnSODs, by virtue of a nonspecific peroxidase activity, may peroxidize spin trapping agents and thus give the appearance of catalyzing OH. production from H2O2. There is a glycosylated, tetrameric Cu, ZnSOD in the extracellular space that binds to acidic glycosamino-glycans. It minimizes the reaction of O2- with NO. E. coli, and other gram negative microorganisms, contain a periplasmic Cu, ZnSOD that may serve to protect against extracellular O2-. Mn(III) complexes of multidentate macrocyclic nitrogenous ligands catalyze the dismutation of O2- and are being explored as potential pharmaceutical agents. SOD-null mutants have been prepared to reveal the biological effects of O2-. SodA, sodB E. coli exhibit dioxygen-dependent auxotrophies and enhanced mutagenesis, reflecting O2(-)-sensitive biosynthetic pathways and DNA damage. Yeast, lacking either Cu, ZnSOD or MnSOD, are oxygen intolerant, and the double mutant was hypermutable and defective in sporulation and exhibited requirements for methionine and lysine. A Cu, ZnSOD-null Drosophila exhibited a shortened lifespan.

Superoxide Radical and Superoxide Dismutases

The plant alkaloids comprise a broad grouping of compounds, many of which exhibit drug action in man (Robinson, 1968) A subclassification is the tetrahydroisoquinoline (TIQ) group, which contains compounds that are related structurally to the catecholamines, viz dopamine (DA), norepinephrine (NE) and epinephrine (E) The main thesis of this paper is that a group of TIQ alkaloids can be biosynthesized in people during alcohol intake, and that these substances can then function as false adrenergic transmitters (Cohen and Collins, 1970) By interfering with adrenergic mechanisms in the brain and in the periphery, biosynthesized TIQ alkaloids may be capable of altering mood and behavior In this way, they may play a role during alcohol intoxication and in post-intoxication states

A Role for Tetrahydroisoquinoline Alkaloids as False Adrenergic Neurotransmitters in Alcoholism

6-Hydroxydopamine and its corresponding ortho- and para-quinones were injected intraperitoneally into male Swiss-Webster mice. Measurements made 72 h after injection showed that all three compounds caused a decrease in the uptake of [3H]norepinephrine into slices of mouse heart tissue in vitro, a decrease in the endogenous content of heart norepine-phrine, and a disappearance of the adrenergic nerve plexus of the mouse iris as viewed by fluorescence histochemistry. These data suggest that both the ortho- and para-quinones of 6-hydroxydopamine are capable of producing a chemical sympathectomy similar to that caused by 6-hydroxydopamine.

Evidence for degeneration of sympathetic nerve terminals caused by the ortho- and para-quinones of 6-hydroxydopamine.

Tetrahydroisoquinoline (TIQ) alkaloids can be formed from catecholamines by spontaneous condensation at neutral pH with aldehydes, such as formaldehyde or a ~ e t a l d e h y d e . ~ J ~ J ~ Some TIQ structures are shown in FIGURE 1. TIQs might be synthesized in man during ingestion of alcoholic beverages. This could follow from the reaction of endogenous catecholamines with the acetaldehyde or formaldehyde that is generated during the metabolism of ethanol or methanol, respectively. Spontaneous condensation reactions could lead to the presence of localized concentrations of TIQs in the adrenal medulla as well as in catecholaminergic nerve terminals in the brain and in the sympathetic nervous system. It has been suggested that biosynthesized TIQs might be capable of acting as “false” adrenergic This paper is concerned with some molecular pharmacological properties of TIQ alkaloids that can be derived from dopamine (DA) , norepinephrine (NE) , and epinephrine (E) . It will be shown that their properties are consistent with the concept that the TIQs can act as false transmitters. In in vitro experiments with isolated rat irides,3 we were able to show that 6,7-dihydroxy-TIQ (the condensation product of dopamine with formaldehyde) can be taken up and accumulated by the sympathetic nerve plexus in the iris. Animals were first treated with reserpine or a-methyl-p-tyrosine in order to deplete the irides of their endogenous stores of NE. Then the irides were incubated at 37OC with various concentrations (0.1 to 10.0 p g per ml) of DA, N E or 6,7-dihydroxy-TIQ. Subsequently, the irides were rinsed briefly in fresh medium to remove extracellular and loosely bound amines. Finally, they were analyzed by fluorescence microscopy with the Falck-Hillarp method to visualize the stored amines; in this method,5 6,7-dihydroxy-TIQ is a nonfluorescent intermediate in the formation of a fluorophore from DA. 6,7 Dihydroxy-TIQ was highly localized in the adrenergic nerve plexus, particularly in the varicosities, which are sites of large numbers of amine-storage vesicles. It was estimated from fluorescence intensity that the accumulation of 6,7-dihydroxy-TIQ was greater than that for DA, but about I/lOth that for NE. The nerve terminals concentrated the TIQ about 100-1,000-fold from the medium. These data show that a strong uptake and storage mechanism exists for TIQs in peripheral sympathetic nerve. More recently, we have been able to show by electron microscopy that 6,7-dihydroxyTIQ is stored in the dense core vesicles that normally bind NE in the rat iris.14 These data are consistent with the notion that TIQs may be capable of acting as false adrenergic neurotransmitters. In other experiments15 radioactive 3H-6,7-dihydroxy-TIQ was prepared from 3H-DA by condensation with formaldehyde. This was administered intravenously to mice and rats (100 pCi/kg). The 3H-TIQ was isolated from organs with syrnpathetic nerve innervation such as the heart, submaxillary glands and irides.

Gerald Cohen

Papers

A Role for Tetrahydroisoquinoline Alkaloids as False Adrenergic Neurotransmitters in Alcoholism

Evidence for degeneration of sympathetic nerve terminals caused by the ortho- and para-quinones of 6-hydroxydopamine.

Tetrahydroisoquinoline alkaloids: uptake, storage, and secretion by the adrenal medulla and by adrenergic nerves.

Tetrahydroisoquinolines and the catecholamine-binding granules of the adrenal medulla

The inhibition of 3H-biogenic amine uptake by 5,6-dihydroxytryptamine: A comparison with the effects of 6-hydroxydopamine