Koichi Itakura

Detection of lipofuscin-like fluorophore in oxidized human low-density lipoprotein. 4-hydroxy-2-nonenal as a potential source of fluorescent chromophore.

It has recently been shown that the lipid peroxidation product 4‐hydroxy‐2‐nonenal (HNE) forms a fluorescent hydroxyiminodihydropyrrole derivative with the ϵ‐amino group of lysine residue. In this study, we raised a monoclonal antibody (mAb2C12) directed to the fluorophore–protein conjugate and found that the antibody was specific to the chromophore structure of the compound. Immunohistochemical analysis of atherosclerotic lesions from the human aorta showed that the fluorophore was indeed present in the lesions, in which intense positivity was primarily associated with macrophage‐derived foam cells and thickening of the neointima of the arterial walls. Antigenic materials were also detected in the oxidatively modified low‐density lipoprotein (LDL) with Cu2+ and in the oxidatively modified bovine serum albumin with an iron/linoleic acid autoxidation system, indicating that the HNE, which originated from the peroxidation of polyunsaturated fatty acids, could be a potential source of the fluorescent chromophore in oxidized LDL.

The Hydroxyl Radical Generated by an Iron(II)/EDTA/Ascorbate System Preferentially Attacks Tryptophan Residues of the Protein

Iron(II)/EDTA/ascorbate-mediated oxidative damage to specific amino acid residues (tryptophan) of serum albumin was studied. The active species generated by Fe(II)/EDTA/ascorbate preferred to react with tryptophan residues rather than histidine or other amino acids. The observation of preferential damage to tryptophan residues of the protein was fully suported by a model experiment using a tryptophan analogue. The reaction of Fe(II)/EDTA/ascorbate to the protein was significantly suppressed by mannitol and dimethysulfoxide, suggesting the participation of the hydroxyl radical generated via Fenton’s reaction. The result was supported by the hydroxyl radical assay using 2-deoxyribose.

Formation of diastereoisomeric 3a-hydroxypyrroloindoles from a tryptophan residue analog mediated by iron(II)-EDTA and l-ascorbate

Oxygenation of a tryptophan residue analog by ascorbate in the presence of catalytic amounts of iron(II) and ethylenediaminetetraacetic acid (EDTA) has been studied. Under physiological conditions, reaction of the tryptophan derivative (N-t-butoxycarbonyl-L-tryptophan) with Fe(II)-EDTA and ascorbate resulted mainly in the oxygenation of the indole moiety of the substrate. In this reaction, cis and trans diastereoisomeric alcohols 3a-hydroxy-1-t-butoxycarbonyl-1,2,3,3a,8,8a-hexahydropyrrolo[2,3- b]indoles have been successfully identified in the metal-catalyzed free radical oxidation of indole compounds. Hydroxylation at C-5 and C-6 and a ring opening reaction between C-2 and C-3 have also been confirmed. The reaction of Fe(II)-EDTA/ascorbate with the tryptophan derivative was apparently nonselective with regard to position and was significantly suppressed by the hydroxyl radical scavengers (mannitol and dimethylsulfoxide), suggesting the participation of the hydroxyl radical as the actual oxidizing species.

A novel tryptophan dioxygenation by superoxide

Abstract The reactions of N -acyl-L-tryptophans, ( 1 ) and ( 2 , with O 2 − afforded their corresponding 2,3-bond cleavage compounds, ( 5 ) and ( 7 ), as the major products. On the other hand, the reactions of N -acyl-L-tryptophan alkylamides, ( 3 ) and ( 4 ), with O 2 − afforded their corresponding dioxindoles, ( 8 ) and ( 9 ), as the major products. A similar reactivity difference was observed for tryptophan-containing dipeptides, ( 10 ) and ( 11 ).