Kinetic studies on the hydroxylation of p-coumaric acid to caffeic acid by spinach-beet phenolase

1. A spectrophotometric assay is described that enables the hydroxylation of p-coumaric acid to caffeic acid, catalysed by spinach-beet phenolase, to be followed continuously. 2. Initial-velocity and inhibitor studies indicate that the order of substrate addition is oxygen, p-coumaric acid and elect...

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Bibliographic Details
Published in:Biochemical journal 1975-08, Vol.149 (2), p.447-461
Main Authors: McIntyre, R J, Vaughan, P F
Format: Article
Language:English
Subjects:
Ascorbic Acid - pharmacology
Benzoates - pharmacology
Caffeic Acids - pharmacology
Catechol Oxidase - metabolism
Cinnamates - metabolism
Coumaric Acids - metabolism
Kinetics
Mathematics
NAD
Oxygen
Plants - enzymology
Pteridines - pharmacology
Spectrophotometry, Ultraviolet
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Summary:1. A spectrophotometric assay is described that enables the hydroxylation of p-coumaric acid to caffeic acid, catalysed by spinach-beet phenolase, to be followed continuously. 2. Initial-velocity and inhibitor studies indicate that the order of substrate addition is oxygen, p-coumaric acid and electron donor, with an irreversible step separating the binding of each substrate. 3. Caffeic acid is most likely to act as electron donor at the active site; other electron donors, such as ascorbic acid, NADH and dimethyltetrahydropteridine, function mainly to recycle cofactor amounts of caffeic acid. 4. A reaction scheme, consistent with these data, is proposed.
ISSN:0264-6021
0306-3283
1470-8728
DOI:10.1042/bj1490447