Klaus Zinner

Generation of electronic energy in the peroxidase catalyzed oxidation of indole-3-acetic acid

Summary The horseradish peroxidase-catalyzed aerobic oxidation of indol-3-acetate results in the conversion of the enzyme to a green form. The spectral changes observed after the oxidation of small amounts of substrate may be reproduced approximately by irradiation of the enzyme at 290 nm. The possibility that electronic energy is generated in the indoleacetate/peroxidase/0 2 system, and is responsible for the change is supported by the chemiluminescence, albeit very weak, observed in the presence of sodium 9,10-dibromoanthracene-2-sulfonate, and of eosin. It appears that the chemienergized species is indol-3-aldehyde in its triplet state.

CHEMIENERGIZED SPECIES IN PEROXIDASE SYSTEMS

Abstract— Several hemeprotein‐catalyzed reactions generate products of the type expected from the cleavage of a high energy intermediate. For some systems, the formation, in high yield, of a carbonyl compound in its excited triplet state has been firmly established on the basis of (i) equivalence of the chemiluminescence and phosphorescence spectra of the expected products; (ii) energy transfer to sensitizers containing heavy atoms and (iii) occurrence of photoproducts. The excited species appears to be generated within the enzyme and shielded from quenching by oxygen. It may be quenched, however, via long‐range triplet‐singlet energy transfer.

ELECTRONICALLY EXCITED SPECIES IN THE PEROXIDASE CATALYZED OXIDATION OF INDOLEACETIC ACID. EFFECT UPON DNA AND RNA

Abstract— The electronically excited species generated in the peroxidase (oxidase) catalyzed oxidation of the plant hormone indole‐3‐acetic acid is an excited state of indole‐3‐carboxaldehyde.

CHEMILUMINESCENCE FROM THE OXIDATION OF AUXIN DERIVATIVES

Abstract— The thiophenyl ester of indole‐3‐acetic acid and indole‐3‐acetonitrile produce chemiluminescence in aerated dimethylsulfoxide in the presence of potassium t‐butoxide. The emitter is the aromatic aldehyde. In the case of acetonitrile, the other product expected from the cleavage of an intermediate dioxetane, cyanate/isocyanate, has also been identified. Other auxins also chemiluminesce under similar conditions, but the emitters have not been properly identified.

Generation of electronic energy in the myoglobin-catalyzed oxidation of acetoacetate to methylglyoxal.

Abstract The myoglobin- or peroxidase-catalyzed aerobic oxidation of acetoacetate to methylglyoxal produces a very weak emission. Light production, methylglyoxal formation, and O 2 uptake strictly correlate with each other. The excited species first formed appears to be triplet methylglyoxal. Formation of the latter species is supported by the increased light emission observed in the presence of very low concentrations of certain sensitizers which contain heavy atoms and have low-lying excited states. In an aprotic solvent the emitter is excited methylglyoxal. The results strongly support the inference that by catalyzing the reaction, myoglobin is damaged by a “photochemistry without light” effect. It is the consequence of the formation of excited methylglyoxal in a major process.

Indole-3-pyruvic acid as a potential luciferin

Abstract Indole-3-pyruvic acid luminesces in aerated dimethyl-sulfoxide solutions in the presence of potassium tert-butoxide. The chemiluminescence spectrum indicates the occurrence of multiple bands whose relative intensities change with time. This behaviour is connected with the presence of two forms of indole-pyruvic acid and with two different reactions, namely at the side chain giving indole-3-carboxaldehyde and at the indole nucleus giving ultimately a product of the N-formyl-kynurenine type. The results suggest that indole-pyruvate is a potential luciferin. This inference is strengthened by the fact that it can originate “in vivo” both indole-aldehyde and oxalate. The reaction at the indole nucleus is tentatively considered a model for tryptophan dioxygenase and related systems.

Generation of electronically excited aromatic aldehydes in the peroxidase catalyzed aerobic oxidation of aromatic acetaldehydes

Abstract The peroxidase catalyzed aerobic oxidation of aromatic acetaldehydes has been investigated with regard to the formation of electronically excited states because it generates the products expected from the cleavage of an intermediate dioxetane, that is, the aromatic aldehyde and formic acid. Emission was detected with the liquid scintillation counter. Integrated emission, indole-3-aldehyde formation, and O2 uptake strictly correlate with each other, unequivocally indicating that the aromatic aldehyde is generated electronically excited. Although the quantum yield of emission is approximately 5×10−9, the yield of chemiexcitation must be several orders of magnitude higher.

Emission from singlet oxygen during the peroxidase-catalyzed oxidation of malonaldehyde.

Malonaldehyde is formed during lipid peroxidation [l] and is further metabolized [2]. The study of reactions that involve malonaldehyde is of multiple biochemical interest [3]. Because it has a highly activated -CH2 group, malonaldehyde qualifies very well as a substrate for peroxidase (acting as an oxidase). As a consequence, peroxidase may convert malonaldehyde to electronically excited products [4], which in turn, may be involved in detrimental effects.

Oxidation of isonicotinic acid hydrazide by the peroxidase system. The formation of an excited product.

Abstract The tuberculostatic and carcinogenic drug isonicotinic acid hydrazide (“isoniazid”) is oxidized to pyridine-4-carboxaldehyde by the horseradish peroxidase/Mn 2+ /O 2 system. Eosin and related sensitizers greatly accelerate the reaction and generate light detectable with the liquid scintillation counter or with the photon counter. If the isoniazid concentration is raised, the rate and extent of O 2 uptake are increased, but above a certain concentration of isoniazid, emission is reduced and even suppressed. The strong quencher of triplet eosin, potassium ferricyanide, abolished both effects of eosin, that is, catalysis and light emission. Superoxide dismutase at high concentrations partially suppressed the emission and almost totally removed the catalytic effect. It is tentatively proposed that the isoniazid/peroxidase/Mn 2+ /O 2 system efficiently produces the aldehyde in the triplet state, which in turn transfers energy to eosin. Because of the presence of oxygen, only a small yield of triplet eosin is obtained and only a small fraction of these triplet eosin molecules is able to react with isoniazid. Nevertheless, it will contribute efficiently to a cyclic process of oxidation of the isoniazid.

Electron exchange chemiluminescence from a sterically stabilized cyclobutadiene-1,2-dioxetane

Abstract The rather stable 1,2-dioxetanes ( 2 ) and ( 3 ), derived from the sterically stabilized cyclobutadiene ( 1 ), exhibit distinct enhanced chemiluminescence behavior, namely energy transfer chemiluminescence (ETC) for ( 2 ) and electron exchange chemiluminescence (EEC) for ( 3 ).