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Biomedical subjects

G Cilento

Publications and source records attributed to G Cilento.

At least 37 records · Page 2Linked to original sources
PubMed1989

Schiff base formation with amino acids enhances light emission and damage induced in neutrophils by phenylacetaldehyde.

The light emission and the loss of cell viability observed when phenylacetaldehyde is added to neutrophils are greatly enhanced when phenylacetaldehyde is administered as a Schiff base with amino acids. As in the case of phenylacetaldehyde, the Schiff base undergoes an intracellular, myeloperoxidase-catalyzed, oxygen-consuming process. Sonication of the cells enhances the emission. With both the free aldehyde and the Schiff bases, the emission spectrum peaks in the 490 nm region, whereas optically excited neutrophils and spent reaction mixtures show maximal emission elsewhere. Apparently, the primarily formed excited species (triplet benzaldehyde) either specifically transfers excitation energy to a component that makes only a minor contribution to the luminescence spectrum of the cells or initiates a process which is itself emissive, e.g. lipid peroxidation. As in the case of phenylacetaldehyde, the oxidation of the Schiff bases excites chlorophyll taken up by neutrophils. Loss of cell viability is likely to be related to in situ generation of excited species.

Acetaldehyde↗
PubMed1989

Generation of triplet carbonyl compounds during peroxidase catalysed reactions.

Peroxidases, acting as oxidase upon appropriate substrates, generate carbonyl compounds in the electronically excited triplet state. These excited species can transfer energy as demonstrated by the appearance of the acceptor fluorescence or induced photochemistry concomitant with the disappearance of phosphorescence. Chlorophyll, an efficient emissive acceptor, either naturally present or artificially incorporated into organelles and cells, allows the in situ detection of biologically generated excited species. With neutrophils, the myeloperoxidase promoted acetone phosphorescence can readily be detected. In other cases, e.g. triplet benzaldehyde, it is possible to observe emission from lipid peroxidation initiated by the triplet carbonyl compound.

Acetaldehyde↗
PubMed1989

Alpha-oxidation of alpha-hydroxyfatty acids in rat brain. Possible involvement of an alpha-peroxylactone.

Combined--but not individual--microsomal and supernatant fractions obtained from rat brains not only consume oxygen but also provoke emission from added chlorophyll. These results are consistent with literature data (Levis and Mead, J. Biol. Chem. 239, 77 [1964]) for trapping of radioactive 14CO2 following addition of alpha-hydroxy-[1-14C]stearic acid. The most plausible explanation for emission is the interaction of chlorophyll with an alpha-peroxylactone. An intermediary alpha-peroxylactone in alpha-oxidation is consistent with other available data (Salim-Hanna, Campa and Cilento, Photochem. Photobiol. 45, 849 [1987]; Campa, Salim-Hanna and Cilento, Photochem. Photobiol. 49, 349 [1989]) and, on chemical grounds, provides a feasible route to the final products.

Animals↗
PubMed1988

Photobiochemistry without light.

Efficient excited state formation - much higher than that hitherto expected - may occur in organelles and in intact cells. Excited triplet states can be enzymatically generated in high yields by different routes. An example is the oxidation of isobutanal to acetone and formic acid, catalyzed by horseradish peroxidase. Other enzymatic systems that generate triplet carbonyls are linear aliphatic aldehydes when oxidized by peroxidase/O2, or the indole-3-acetic acid/peroxidase/O2-reaction. The latter is widespread in plants. This new field - photobiochemistry without light - has led to a growing awareness of the idea that cells may utilize excited states to trigger photochemical processes even in the dark. Such phenomena are of considerable importance, also for the understanding of weak photon emission from biological systems.

Acetone↗
PubMed1987

Oxidation of phenylpyruvic acid.

Mn2+ catalyzes the aerobic oxidation of phenylpyruvic acid. Benzaldehyde and oxalate are the major products, the former being generated to some extent in an excited state, as indicated by chlorophyll-sensitized emission. Both oxygen consumption and emission are enhanced by addition of horseradish peroxidase. In the presence of the enzyme, halogen-containing xanthene dyes also sensitize the emission. From the values of the benzaldehyde/oxalate product ratio, it is inferred that two oxidation pathways are operative. One of these proceeds via a dioxetane intermediate and is responsible for the excited benzaldehyde; the other, which involves an alpha-keto-beta-peroxylactone, does not produce oxalate. The enzyme appears to favour the dioxetane route. The relative importance of these routes in biological systems is discussed.

Benzaldehydes↗
PubMed1987

Peroxidase-promoted aerobic oxidation of 2-nitropropane: mechanism of excited state formation.

Using sensitized emission, the horseradish peroxidase-catalyzed aerobic oxidation of the toxic pollutant 2-nitropropane to nitrite and acetone is shown to produce the latter in the electronically excited triplet state. In turn, this chemiexcitation implies a hydroperoxide precursor. Taking into account the stoichiometry of the reaction and available isotopic data it is inferred that the hydroperoxide reacts with a second molecule of the substrate (aci form). While triplet acetone formed from isobutanal (enol form) is generated within the enzyme, in the present case triplet acetone is formed in the bulk solution.

Acetone↗
PubMed1987

Generation of electronically excited states in situ. Polymorphonuclear leukocytes treated with phenylacetaldehyde.

In polymorphonuclear leukocytes phenylacetaldehyde promotes an intracellular O2 consuming process in which myeloperoxidase participates. The reaction is accompanied by lipid peroxidation as shown by both malondialdehyde formation and biphasic light emission. The lipid peroxidation appears to be induced by intracellularly generated triplet benzaldehyde. When chlorophyll-a is solubilized in the leukocytes, biphasic emission is observed in the red, demonstrating that the excited species formed in lipid peroxidation transfer their energy to chlorophylls bound to the cell. The energy transfer process is efficient and does not occur by radiative transfer.

Acetaldehyde↗
PubMed1986

Interaction between enzyme-generated triplet carbonyls and molecules intercalated into DNA.

The phosphorescence from enzyme-generated and -protected triplet acetone is very efficiently quenched by dyes intercalated into DNA. The process is unlikely to be due to energy transfer and is tentatively ascribed to electron transfer occurring within the DNA helix complex with the acting enzyme. This quenching markedly protects DNA from breaks induced by triplet acetone. In the case of some barely emissive enzyme-generated triplet carbonyl species, it is possible to detect a weak emission resulting from the interaction with dye X DNA; this emission may be associated with back electron transfer.

Acetone↗
PubMed1986

Enols of aldehydes in the peroxidase/oxidase-promoted generation of excited triplet species.

General (acid and base) or specific (fluoride ion) catalysis generates the enol of isobutanal and propanal from the corresponding trimethylsilyl enol ethers. The enols are directly rapidly oxidized by peroxidase (acting as an oxidase) to triplet acetone or triplet acetaldehyde, respectively, and formic acid. Due to the faster rate of reaction and the absence of quenching by excess aldehyde, the excited carbonyl emits more strongly than when the aldehyde itself is the substrate. With both enols the emission is pure phosphorescence. Both triplet acetone and triplet acetaldehyde are generated within the enzyme, as shown by the different quenching by D- and L-tryptophan, and are somewhat protected from oxygen quenching, as attested by the very fact that phosphorescence is observed. The use of enol precursors as substrates opens wide possibilities for photochemical investigations in the absence of light over a much broader range of experimental conditions.

Acetone↗
PubMed1985

Peroxidase-catalyzed formation of triplet acetone and chemiluminescence from isobutyraldehyde and molecular oxygen.

It has been established that the horseradish peroxidase/O2/isobutyraldehyde (IBAL) system leads to triplet acetone and formic acid formation followed by phosphorescence of the triplet acetone (see, for example, Bechara, E.J.H., Faria Oliveira, O.M.M., Durán, N., Casadei de Baptista, R., and Cilento, G. (1979) Photochem. Photobiol. 30, 101-110). In this paper many of the mechanistic details are established. The reaction is initiated by the autoxidation of IBAL to form the peracid (CH3)2CHC = O(OOH). The peracid converts horseradish peroxidase into compound I which in turn is converted into compound II by abstracting the alcoholic hydrogen atom from the enol form of IBAL. This creates a free radical with two resonance forms. (Formula: see text) Addition of molecular oxygen to the latter resonance form creates a peroxy radical which abstracts a hydrogen atom near the active site of the enzyme. The newly formed alpha-peroxide in turn forms a dioxetane-type of intermediate which rapidly decomposes into triplet acetone and formic acid. Compound II reacts with the enol by the same pathway as compound I. Thus native horseradish peroxidase is regenerated. The hydrogen atom abstraction near the enzyme active site may occur directly from ethanol, present to solubilize IBAL or from a group on the enzyme, in which case ethanol participates in a repair mechanism. Phosphate buffer is necessary because it catalyzes the keto-enol conversion of IBAL. Thus horseradish peroxidase participates in a normal peroxidatic cycle. The only chain reaction is the uncatalyzed autoxidation of IBAL, most of which occurs prior to the mixing of IBAL with the oxygenated horseradish peroxidase solution.

Acetone↗
PubMed1984

On the mechanism of peroxidase-catalyzed chemiluminescence from isobutyraldehyde.

The reaction of isobutyraldehyde with dissolved oxygen catalyzed by horseradish peroxidase has been studied from the standpoint of determining the rate-limiting factor under a variety of conditions. Chemiluminescence from the product triplet acetone and rate of oxygen uptake were determined in simultaneous experiments. The reaction is initiated by the peracid obtained from the uncatalyzed autoxidation of the aldehyde; and under certain conditions the amount of peracid is also rate-limiting in the steady-state portion of the reaction. Under other conditions the total amount of enzyme and under still others the rate of formation of enol from the parent aldehyde controls the rate.

Aldehydes↗
PubMed1984

Excitation of micelle-solubilized chlorophyll during the peroxidase-catalyzed aerobic oxidation of isonicotinic acid hydrazide.

Addition of micelle (hexadecyl-trimethylammoniumbromide)-solubilized chlorophyll alpha to the isoniazid/peroxidase/Mn2+/O2 system promotes light emission, identified as chlorophyll fluorescence. Based on O2 consumption, the quantum yield of chlorophyll excitation to the S1 state exceeds 6 X 10(-6). At least part of the excitation has its origin in the conversion of an intermediate--presumably a diazene--to pyridine-4-carboxaldehyde. On the basis of the present and earlier results [K. Zinner, C. C. C. Vidigal, N. Durán, and G. Cilento (1977) Arch. Biochem. Biophys. 180, 452-458], it is inferred that isoniazid, an important chemotherapeutic and also a carcinogenic agent, can lead to a substantial generation of electronically excited states.

Cetrimonium↗
PubMed1984

Low-level luminescence from microsomes exposed to enzymatic systems that generate triplet species.

Microsomes exposed to the propanal/horseradish peroxidase/O2 system develop a weak chemiluminescence. The underlying process is distinct from that occurring during lipid peroxidation because the emission intensity peaks at around 560 nm, rather than in the red, and no malonaldehyde is formed. Triplet acetaldehyde appears to be responsible for the induction of the process, which in turn leads to excitation of a component in microsomes, possibly a flavoprotein.

Aerobiosis↗