Identification of skatolyl hydroperoxide and its role in the peroxidase-catalysed oxidation of indol-3-yl acetic acid.
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.
Gazarian
I G
IG
Nitrogen Fixation Laboratory, John Innes Centre, Colney, Norwich NR4 7UH, U.K.
Lagrimini
L M
LM
Mellon
F A
FA
Naldrett
M J
MJ
Ashby
G A
GA
Thorneley
R N
RN
D002248:Carbon Monoxide / Q000737:chemistry; D002374:Catalase / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D005609:Free Radicals / Q000737:chemistry; D007210:Indoleacetic Acids / Q000737:chemistry*; D007211:Indoles / Q000138:chemical synthesis; D007700:Kinetics; D013058:Mass Spectrometry; D010084:Oxidation-Reduction; D010545:Peroxides / Q000737:chemistry* / Q000302:isolation & purification; D012862:Skatole / Q000031:analogs & derivatives* / Q000737:chemistry / Q000302:isolation & purification; D013056:Spectrophotometry, Ultraviolet; D013482:Superoxide Dismutase / Q000737:chemistry
D005609:Free Radicals; D007210:Indoleacetic Acids; D007211:Indoles; D010545:Peroxides; C113479:skatolyl hydroperoxide; C012381:indole-3-carbaldehyde; D002248:Carbon Monoxide; D012862:Skatole; D002374:Catalase; D013482:Superoxide Dismutase