Characterization of Polyphenol Oxidase from Photosynthetic and Vascular Lettuce Tissues (Lactuca sativa)

To examine the undesired enzymatic browning in iceberg lettuce(lactuca sativa L.), polyphenol oxidase (PPO) from vascular and photosynthetic tissues was characterized. PPO activity was determined by measuring dioxygen consumption with a Clark electrode. The enzyme in photosynthetic and vascular tiss...

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Bibliographic Details
Published in:Journal of agricultural and food chemistry 1994-07, Vol.42 (7), p.1428-1433
Main Authors: Heimdal, Hanne, Larsen, Lone M., Poll, Leif
Format: Article
Language:English
Subjects:
actividad enzimatica
activite enzymatique
Biological and medical sciences
catechol oxidase
catechol oxydase
catecol oxidasa
enzymic activity
feuille
Food industries
Fruit and vegetable industries
Fundamental and applied biological sciences. Psychology
hojas
lactuca sativa
leaves
molecular weight
peso molecular
plant vascular system
poids moleculaire
sistema vascular de la planta
systeme vasculaire des plantes
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Summary:To examine the undesired enzymatic browning in iceberg lettuce(lactuca sativa L.), polyphenol oxidase (PPO) from vascular and photosynthetic tissues was characterized. PPO activity was determined by measuring dioxygen consumption with a Clark electrode. The enzyme in photosynthetic and vascular tissues had native molecular weights of >/= 1,50 000 and >/= 136 000, respectively. In addition, two PPO-active bands(40000 and 46000) were found invascular tissue only. The following enzyme characteristics were found for PPO from both vascular and photosynthetic lettuce tissues: substrate specificity exclusively for o-dihydroxy substrates; pI 3.6; pH optimum 5-8; temperature optimum 25-35 degrees C; pH stability 5-8 for 20 h at 5 degrees C; temperature stability 0-70 degrees C for 5 min. Michaelis-Menten characteristics for a range of o-dihydroxy substrates and dioxygen were determined. The enzyme in vascular and photosynthetic tissues in lettuce could be classified as a 1,2-benzenediol:oxygen oxidoreductase (EC 1.10.3.1).
ISSN:0021-8561
1520-5118
DOI:10.1021/jf00043a008