Plant hormone ethylene is a Norrish type II product from enzymically generated triplet 1-butanal.

Abstract

The peroxidase-catalyzed aerobic oxidation of a linear aldehyde, leading to the next lower homologue in the triplet state, is accompanied by Norrish type H product ethylene when the substrate is pentanal. This system appears to provide an example of "photobiochemistry without light" because ethylene is a plant hormone and is formed in lipid peroxidation when the recurrent oxidation of linear aldehydes occurs. In this work, we report a study ofthis reaction as a function of aldehyde chain length and show that, when pentanal is the substrate, the reaction is accompanied by the formation of the predicted Norrish type II (5) product ethylene. MATERIALS AND METHODSThe aldehydes (Fluka), HRP (types VI, I, and II; Sigma), and eosine (Merck) were commercially available. Aldehydes were stored under N2 at -20°C. The trimethylsilylenol ethers of pentanal and of butanal were prepared according to Cazeau et al. (6).Unless otherwise stated, HRP type VI was used throughout the work; it was sufficiently pure, as attested to by the reproducibility of results in this and in all previous work, even when subjected to further purification. The absence of detectable amounts of ethylene in the absence of aldehydes (see Results and Discussion) indicates that the HRP used contains no ethylene-producing endogenous substrate.Comparative oxygen consumption by the C2-C6 aldehydes in the presence of HRP necessary for the experiments with eosine was ascertained in a Warburg apparatus. The (slow) rate of oxygen uptake was as follows: C2 < C3 < C4 = C5 = The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.C6. When the trimethylsilylenol ethers were used as substrates, oxygen uptake was measured in a Yellow Springs Instruments model 53 oxygen monitor.The experiments with eosine were done at 40°C in 0.5 M phosphate/0.04 M sodium pyrophosphate buffer, pH 7.4/0.5 M ethanol/10 ,uM eosine/1 x 10-4 M hydrogen peroxide/2 mM, 4 mM, or 8 mM aldehyde; total volume was 3 ml. The reaction was initiated by HRP addition (final concentration, 2 ,uM); under these conditions eosine is stable. Light emission was measured in a Hamamatsu model TUC-767 photon counter provided with a Hamamatsu R-562 photomultiplier tube.The experiments with the trimethylsilylenol ethers of pentanal and of butanal were done at 37°C in 0.01 M Tris buffer, pH 7.4/2 mM substrate/4 ,uM HRP. The reaction was initiated by adding 1 x 10-4 M hydrogen peroxide. The system was incubated for 10 min in a 124-ml round-bottom flask sealed with a Teflon-lined rubber septum.The experiments with butanal and propanal were done at 37°C in 0.5 M phosphate buffer, pH 7.4/0.04 M sodium pyrophosphate/1 x 10-4 M hydrogen peroxide/8 mM aldehyde (freshly distilled). The reaction was initiated by adding 1 X 10-4 M hydrogen peroxide. The incubation (as above) was for 50 min. Regarding hydrogen peroxide use in all these systems, note that hydrogen per...

Temperature Factor Affecting the Abscission Response of Mature Fruit and Leaves to CMN-Pyrazole and Ethephon in `Hamlin' Oranges

“…CMNP may wound peel early after application and before visual peel damage appears. If wound ethylene immediately after application is responsible for initiating abscission, the ethylene could be derived from peroxidized membranes damaged by CMNP (Knudson et al, 1994). The amount of ethylene necessary to initiate abscission is likely to be below the detection limit using conventional gas chromatography.…”

Chemi- and Bioluminescence of Cyclic Peroxides

“…Several works were then successfully carried out to prove it (see the review on the topic by Baader et al and references therein). Some illustrative examples are the detection of thymine dimers in the calf thymus DNA treated with trimethyl-1,2-dioxetane without UV radiation, ,, the oxidative DNA damage by radicals generated via the chemiexcitation of ketones, the photo-oxidation of guanosine and the acyclovir antiviral drug, the production of the plant hormone ethylene from enzymatically generated triplet 1-butanal, the electrocyclic ring closure of the tropolonic alkaloid colchicine into lumicolchicines in underground corms of autumn crocus (Colchicum autumnale), or the opening of the B-ring of protovitamins D through triplet sensitization in the isobutyraldehyde/peroxidase/O 2 system . By using the horseradish peroxidase-catalyzed aerobic oxidation of isobutyraldehyde to formic acid and triplet acetone, Cilento and co-workers could excite or chemically modify several biological energy acceptors such as xanthene dyes, day-period mediators in phototropism and photoperiodism, chlorophyll, the estrogen diethylstilbestrol with tumorigenic properties, and tetracycline antibiotics with bactericidal activity .…”

1,3-Diene Probes for Detection of Triplet Carbonyls in Biological Systems

“…For example, both alkoxyl radicals and triplet carbonyls (Scheme 2) can undergo isomerizations, R-cleavage, and bimolecular reactions such as hydrogen abstraction and addition to unsaturated compounds. Accordingly, (i) triplet acetone generated either by the thermolysis of tetramethyl-1,2-dioxetane (TMD) or by the HRP-catalyzed oxidation of IBAL by dioxygen was shown to initiate and amplify the peroxidation of both linolenic and arachidonic acid (15) and to abstract hydrogen from the carbohydrate portion of HRP, yielding 2-propanol and pinacol (12), (ii) triplet n-butanal produced by the HRP-catalyzed aerobic oxidation of n-pentanal was reported to undergo Norrish cleavage yielding ethylene, a plant hormone (16), and (iii) cytochrome c-catalyzed generation of triplet benzophenone could be coupled to promotion of oxidative damage to rat liver mitochondrial DNA, phospholipids, and proteins (17).…”

“…With regard to the detection of triplet carbonyls in chemical and enzymatic systems (Scheme 2), triplet-singlet energy transfer experiments using adequate highly fluorescent acceptors, such as eosine or the water-soluble sodium 9,10-dibromoanthracene-2-sulfonate (DBAS) (18), may yield invaluable information. Alternatively, photoproducts from the excited species can be detected, e.g., ethylene and ethanal yielded by triplet n-butanal cleavage (16) or acetone and cyclobutanols obtained from elimination and cyclization reactions of excited 2-hexanone (19). A third possibility is to use chemical and physical quenchers of triplet carbonyls, such as conjugated dienes, indoles, quinones, and tyrosine derivatives (20).…”