Energy transfer from enzymically generated triplet carbonyl compounds to the fluorescent state of flavins

A new approach to problem of enzymatic catalysis based on excited state of proteins and Le Chatelier's principle

A hypothesis is proposed that the energy of an exothermic reaction in an aqueous medium can be used to shift the equilibrium in an endothermic reaction involving hydrated ions. This takes place according to Le Chatelier's principle, and the water dissociation in the homogeneous medium at the protein-water interface gives rise to concentration gradients of ions H(+) and OH(-). The hypothesis implies that the chemical conversion of the substrate into the product is preceded by an attack of hydrated ions on the protein and their association on the protein (an attack of the nucleophilic agent with the subsequent proton addition). This leads to the formation of a cyclic peroxide in an amino acid residue and to the transition C=O-->[C=O](*). The return of carbonyl to the ground state ultimately allows to accumulate a part of the free energy and to use it to bring the enzyme to a state where the conformational energy is higher. Thus, an electronically excited state of a protein is regarded as a state required for dark reactions. This means that, along with the substrate sorption on the protein, the other aspect of the behavior of the dynamic system should be taken into account.

Bacterial luminescence: luminescence mechanism with cyclic peroxide participation and dependence on reactive oxygen species (a hypothesis)

Chemically initiated exchange (CIEE) luminescence reactions were reviewed and a new mechanism of luminescence with peracid as an intermediate is proposed; bacterial luminescence is generally considered to be a case of dioxetane luminescence, or, to be more precise, CIEE-luminescence which includes the generation of a cyclic peroxide. In the hypothesis the monooxygenase reaction (aldehyde -->fatty acid) should not be coupled with emitter generation as is usually believed, but only with the generation of peracid. As to the generation of the emitter, excited flavin, it is likely to occur later, during the interaction of flavin with cyclic peroxide. Its consequence is the breaking of two chemical bonds (O-O and C-C) in the cyclic peroxide and simultaneous generation of 4alpha-hydroxyflavin in exited state. In general, the generation of light includes three stages: 1) the monooxygenase reaction and the concurrent production of peracid; 2) the conversion of peracid to cyclic peroxide; and 3) the interaction of cyclic peroxide with flavin (through the CIEE mechanism).

Lipid peroxidation during the oxidation of haemoproteins by hydroperoxides. Relation to electronically excited state formation

The formation of electronically excited states during hydroperoxide metabolism is analysed in terms of recombination reactions involving secondary peroxyl radicals and scission of the O-O bond of peroxides by haemoproteins, mainly myoglobin. Both processes may be sequentially interrelated, for the cleavage of H2O2 by metmyoglobin leads to the formation of a strong oxidizing equivalent with the capability to promote peroxidation of polyunsaturated fatty acids. The decomposition of lipid hydroperoxides by ferryl-hydroxo complexes, as that formed during the oxidation of metmyoglobin by H2O2, is a source of peroxyl radicals, the recombination of which proceeds with elimination of a conjugated triplet carbonyl or singlet oxygen.

Quenching of enzyme-generated acetone phosphorescence by indole compounds: stereospecific effects of D- and L-tryptophan. Photochemical-like effects

Indole compounds efficiently quench the acetone phosphorescence observed during the horseradish peroxidase catalyzed aerobic oxidation of isobutyraldehyde. Different types of Stern-Volmer plots are observed: linear, linear with two slopes, and downward- and upward-curved plots. The complexity probably stems from the operation of both dynamic and static quenching, coupled with different efficiencies of quenching of various acetone triplet populations. Binding to the enzyme may also occur, especially in the case of L-tryptophan. The different Stern-Volmer behavior of D- and L-tryptophan fully confirms that the acetone triplet is generated within the enzyme and not free in solution. This chiral discrimination toward an enzymically generated electronically excited species is novel. It is tentatively postulated that a long-range triplet-triplet exciton transfer occurs; the excited triplet indole then undergoes photochemical-like alterations.