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Biomedical subjects

R Nakajima

Publications and source records attributed to R Nakajima.

At least 91 records · Page 5Linked to original sources
PubMed1980

The conversion of horseradish peroxidase C to a verdohemoprotein by a hydroperoxide derived enzymatically from indole-3-acetic acid and by m-nitroperoxybenzoic acid.

A verdohemoprotein was formed from Compound I of horseradish peroxidase C upon the addition of about 2 molar equivalents of m-nitroperoxybenzoic acid (mNPBA) or hydroperoxide formed from indole-3-acetic acid during its catalytic oxidation. The formation of the verdohemoprotein occurred via two intermediates which have an absorbance peak at 965 or 940 nm. Carbon monoxide was evolved in the reaction from the 940 compound to the verdohemoprotein. From the kinetic and titration data, the following reaction sequence was proposed. (Formula: see text). The 940 compound could be reduced by dithionite and ascorbate to the ferrous and the ferric enzyme, respectively. The enzyme species that reacted with mNPBA to form the 965 and the 940 compounds was concluded to be Compound I but neither Compound II nor oxyperoxidase (Compound III).

Carbon Monoxide↗
PubMed1979

The mechanism of indole-3-acetic acid oxidation by horseradish peroxidases.

The oxygen-consuming oxidation of indole-3-acetic acid (IAA) occurred much faster in the presence of horseradish peroxidase C (neutral isoenzyme) than in the presence of horseradish peroxidase A (acidic isoenzyme). An intermediate oxidation product of IAA was found to be a hydroperoxide species that reacted with the ferric enzymes to form Compound I at second order rate constants of 6.8 X 10(3) M-1--S-1 for peroxidase A and 2.0 X 10(6) M-1--S-1 for peroxidase C at pH 4.4 The hydroperoxide concentration reached about one-half of the initial IAA concentration at the end of the oxygen-consuming reaction and then decreased slowly. The main intermediate of the enzyme observed during the oxygen-consuming reaction was Compound II, which oxidized IAA to its free radical at rate constants of 1.5 X 10(3) M-1--S1 for peroxidase A and 1.2 times 10(4) M-1--S-1 for peroxidase C at pH 4.4 The results supported the mechanism that the oxygen consumption occurs mainly through the reaction of oxygen with the IAA free radical formed from the peroxidatic oxidation of IAA. The ferric enzymes were not reduced by IAA under strict anaerobic conditions in the presence of carbon monoxide but were reduced upon addition to a small amount of oxygen or hydrogen peroxide to the systems. The results suggested that the ferric enzyme is reduced by the IAA free radical but not by IAA itself. From a comparison of reactivities of oxyperoxidase and Compound II we concluded that the catalytic cycle of ferrous and oxyperoxidases is not involved in the IAA oxidase reaction.

Horseradish Peroxidase↗