Polyphenol oxidase: The chloroplast oxidase with no established function |
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Authors: | Kevin C Vaughn Alan R Lax Stephen O Duke |
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Institution: | Agricultural Research Service, Southern Weed Science Laboratory, P.O. Box 350, Stoneville, MS 38776, USA;USDA, Agricultural Research Service, Southern Regional Research Center, P.O. Box 19687, New Orleans, LA 70179, USA. |
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Abstract: | Vaughn, K. C, Lax, A. R. and Duke, S. O. 1988. Polyphenol oxidase: The chloroplast oxidase with no established function. - Physiol. Plant. 72: 659–665. Polyphenol oxidase (PPO) is an enzyme localized on the thylakoids of chloroplasts and in vesicles or other bodies in non-green plastid types. Although virtually all plastids contain PPO, little or no detectable activity is associated with guard cell and bundle sheath cell chloroplasts. Despite this nearly ubiquitous occurrence, no function for this enzyme has been established. The enzyme is nuclear-encoded and, unlike most chloroplast proteins is not encoded as a larger M, precursor molecule. This lack of a transit peptide sequence may be related to a unique mechanism of uptake, apparently involving inner envelope-derived vesicles. The M, range of most of the PPO forms is 36–45 kDa. PPO is apparently not involved in phenolic biosynthesis but is probably involved with the production of o -quinones during pathogen invasion. A role for PPO as an "oxygen buffer" is postulated, but little concrete data have been collected on any other functional role for this enzyme. |
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Keywords: | Chloroplast flavonoids polyphenol oxidase protein processing and transport |
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