Identification of skatolyl hydroperoxide and its role in the peroxidase-catalysed oxidation of indol-3-yl acetic acid

• Published in: Biochemical journal Vol. 333 ( Pt 1); no. 1; pp. 223 - 232
• Main Authors: Gazarian, I G, Lagrimini, L M, Mellon, F A, Naldrett, M J, Ashby, G A, Thorneley, R N
• Format: Journal Article
• Language: English
• Published: England 01.07.1998
• Subjects: Carbon Monoxide - chemistry; Catalase - chemistry; Chromatography, High Pressure Liquid; Free Radicals - chemistry; Indoleacetic Acids - chemistry; Indoles - chemical synthesis; Kinetics; Mass Spectrometry; Oxidation-Reduction; Peroxides - chemistry; Peroxides - isolation & purification; Skatole - analogs & derivatives; Skatole - chemistry; Skatole - isolation & purification; Space life sciences; Spectrophotometry, Ultraviolet; Superoxide Dismutase - chemistry
• ISSN: 0264-6021; 1470-8728
• DOI: 10.1042/bj3330223

Indol-3-yl acetic acid (IAA, auxin) is a plant hormone whose degradation is a key determinant of plant growth and development. The first evidence for skatolyl hydroperoxide formation during the plant peroxidase-catalysed degradation of IAA has been obtained by electrospray MS. Skatolyl hydroperoxide degrades predominantly non-enzymically to oxindol-3-yl carbinol but in part enzymically into indol-3-yl methanol via a peroxidase cycle in which IAA acts as an electron donor. Skatolyl hydroperoxide is degradable by catalase. Horseradish peroxidase isoenzyme C (HRP-C) and anionic tobacco peroxidase (TOP) exhibit differences in their mechanisms of reaction. The insensitivity of the HRP-C-catalysed reaction to catalase is ascribed to the formation of HRP-C Compound III at the initiation step and its subsequent role in radical propagation. This is in contrast with the TOP-catalysed process in which skatolyl hydroperoxide has a key role. Indol-3-yl aldehyde is produced not via the peroxidase cycle but by catalysis involving ferrous peroxidase. Because indol-3-yl aldehyde is one of the main IAA-derived products identified in planta, we conclude that ferrous peroxidases participate in IAA catalytic transformations in vivo. A general scheme for peroxidase-catalysed IAA oxidation is presented.