Spinach Thylakoid Polyphenol Oxidase : ISOLATION, ACTIVATION, AND PROPERTIES OF THE NATIVE CHLOROPLAST ENZYME
John H. Golbeck,Kirk Cammarata +1 more
TLDR
A large seasonal variation in polyphenol oxidase activity may result from a decrease in enzyme content rather than inhibition of the enzyme present.Abstract:
Polyphenol oxidase activity (E.C. 1.14.18.1) has been found in two enzyme species isolated from thylakoid membranes of spinach chloroplasts. The proteins were released from the membrane by sonication and purified >900-fold by ammonium sulfate precipitation, gel filtration, and ion-exchange chromatography. The enzymes appear to be the tetramer and monomer of a subunit with a molecular weight of 42,500 as determined by lithium dodecyl sulfate gel electrophoresis. The higher molecular weight enzyme is the predominant form in freshly isolated preparations but on aging or further purification, the amount of lower molecular weight enzyme increases at the expense of the higher.Sonication releases polyphenol oxidase from the membrane largely in the latent state. C(18) fatty acids, especially linolenic acid, are potent activators of the enzymic activity. In the absence of added fatty acids, the isolated enzyme spontaneously, but slowly, activates with time.Purified polyphenol oxidase utilizes o-diphenols as substrates and shows no detectable levels of monophenol or p-diphenol oxidase activities. The K(m) values for 3,4-dihydroxyphenylalanine and O(2) are 6.5 and 0.065 millimolar, respectively. Suitable substrates include chlorogenic acid, catechol, caffeic acid, pyrogallol, and dopamine; however, the enzyme is substrate-inhibited by the last four at concentrations near their K(m) A large seasonal variation in polyphenol oxidase activity may result from a decrease in enzyme content rather than inhibition of the enzyme present.read more
Citations
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Copper Active Sites in Biology
Edward I. Solomon,David E. Heppner,Esther M. Johnston,Jake W. Ginsbach,Jordi Cirera,Munzarin F. Qayyum,Matthew T. Kieber-Emmons,Christian H. Kjaergaard,Ryan G. Hadt,Li Tian +9 more
TL;DR: This review presents in depth discussions of all these classes of Cu enzymes and the correlations within and among these classes, as well as the present understanding of the enzymology, kinetics, geometric structures, electronic structures and the reaction mechanisms these have elucidated.
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TL;DR: In this paper, the authors summarized progress in the plant polyphenol oxidases in the period 1978-1986 and reviewed the results of laccases and catechol oxidase.
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Physicochemical properties and function of plant polyphenol oxidase: a review'
Ruhiye Yoruk,Maurice R. Marshall +1 more
TL;DR: An overview of the current understanding of the reaction properties, biochemical characteristics and potential physiological roles of polyphenol oxidase (PPO)-catalyzed browning reactions are presented in this article.
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Sequence and structural features of plant and fungal tyrosinases
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References
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Polyphenol oxidases in plants
Alfred M. Mayer,Eitan Harel +1 more
TL;DR: Two main groups of plant polyphenol oxidases are recognized: the catecholoxidases and the laccases: their purification, subcellular location and protein properties are described.
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