Myoglobin-H2O2 catalyzes the oxidation of β-ketoacids to α-dicarbonyls: mechanism and implications in ketosis

Mining reactive triplet carbonyls in biological systems

Aliphatic triplet carbonyls can be treated as short-lived radicals, since both species share similar reactions such as hydrogen atom abstraction, cyclization, addition, and isomerization. Importantly, enzyme-generated triplet carbonyls excite triplet molecular oxygen to the highly reactive, electrophilic singlet state by resonance energy transfer, which can react with proteins, lipids, and DNA. Carbonyl triplets, singlet oxygen, and radicals are endowed with the potential to trigger both normal and pathological responses. In this paper, we present a short review of easy, fast, and inexpensive preliminary tests for the detection of transient triplet carbonyls in chemical and biological systems. This paper covers direct and indirect methods to look for triplet carbonyls based on their spectral distribution of chemiluminescence, photoproduct analysis, quenching of light emission by conjugated dienes, and enhancement of light emission by the sensitizer 9,10-dibromoanthracence-2-sulfonate ion (DBAS).

Chemiexcitation: Mammalian Photochemistry in the Dark†

Light is one way to excite an electron in biology. Another is chemiexcitation, birthing a reaction product in an electronically excited state rather than exciting from the ground state. Chemiexcited molecules, as in bioluminescence, can release more energy than ATP. Excited states also allow bond rearrangements forbidden in ground states. Molecules with low-lying unoccupied orbitals, abundant in biology, are particularly susceptible. In mammals, chemiexcitation was discovered to transfer energy from excited melanin, neurotransmitters, or hormones to DNA, creating the lethal and carcinogenic cyclobutane pyrimidine dimer. That process was initiated by nitric oxide and superoxide, radicals triggered by ultraviolet light or inflammation. Several poorly understood chronic diseases share two properties: inflammation generates those radicals across the tissue, and cells that die are those containing melanin or neuromelanin. Chemiexcitation may therefore be a pathogenic event in noise- and drug-induced deafness, Parkinson's disease, and Alzheimer's; it may prevent macular degeneration early in life but turn pathogenic later. Beneficial evolutionary selection for excitable biomolecules may thus have conferred an Achilles heel. This review of recent findings on chemiexcitation in mammalian cells also describes the underlying physics, biochemistry, and potential pathogenesis, with the goal of making this interdisciplinary phenomenon accessible to researchers within each field.

Modulation of 1,2-Dicarbonyl Compounds in Postprandial Responses Mediated by Food Bioactive Components and Mediterranean Diet

Glycoxidative stress with the consequent generation of advanced glycation end products has been implied in the etiology of numerous non-communicable chronic diseases. During the postprandial state, the levels of 1,2-dicarbonyl compounds can increase, depending on numerous factors, including characteristics of the subjects mainly related to glucose metabolism disorders and nutritional status, as well as properties related to the chemical composition of meals, including macronutrient composition and the presence of dietary bioactive molecules and macromolecules. In this review, we examine the chemical, biochemical, and physiological pathways that contribute to postprandial generation of 1,2-dicarbonyl compounds. The modulation of postprandial 1,2-dicarbonyl compounds is discussed in terms of biochemical pathways regulating the levels of these compounds, as well as the effect of phenolic compounds, dietary fiber, and dietary patterns, such as Mediterranean and Western diets.

Excited singlet molecular O₂(¹Δg) is generated enzymatically from excited carbonyls in the dark

In mammalian tissues, ultraweak chemiluminescence arising from biomolecule oxidation has been attributed to the radiative deactivation of singlet molecular oxygen [O2 ((1)Δg)] and electronically excited triplet carbonyl products involving dioxetane intermediates. Herein, we describe evidence of the generation of O2 ((1)Δg) in aqueous solution via energy transfer from excited triplet acetone. This involves thermolysis of 3,3,4,4-tetramethyl-1,2-dioxetane, a chemical source, and horseradish peroxidase-catalyzed oxidation of 2-methylpropanal, as an enzymatic source. Both sources of excited carbonyls showed characteristic light emission at 1,270 nm, directly indicative of the monomolecular decay of O2 ((1)Δg). Indirect analysis of O2 ((1)Δg) by electron paramagnetic resonance using the chemical trap 2,2,6,6-tetramethylpiperidine showed the formation of 2,2,6,6-tetramethylpiperidine-1-oxyl. Using [(18)O]-labeled triplet, ground state molecular oxygen [(18)O2 ((3)Σg(-))], chemical trapping of (18)O2 ((1)Δg) with disodium salt of anthracene-9,10-diyldiethane-2,1-diyl disulfate yielding the corresponding double-[(18)O]-labeled 9,10-endoperoxide, was detected through mass spectrometry. This corroborates formation of O2 ((1)Δg). Altogether, photoemission and chemical trapping studies clearly demonstrate that chemically and enzymatically nascent excited carbonyl generates (18)O2 ((1)Δg) by triplet-triplet energy transfer to ground state oxygen O2 ((3)Σg(-)), and supports the long formulated hypothesis of O2 ((1)Δg) involvement in physiological and pathophysiological events that might take place in tissues in the absence of light.