Linked Life Data

16661805

Source:http://linkedlifedata.com/resource/pubmed/id/16661805

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
5
pubmed:dateCreated
2010-6-29
pubmed:abstractText
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.
pubmed:commentsCorrections
pubmed:language
eng
pubmed:journal
pubmed:status
PubMed-not-MEDLINE
pubmed:month
May
pubmed:issn
0032-0889
pubmed:author
pubmed:issnType
Print
pubmed:volume
67
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
977-84
pubmed:dateRevised
2010-9-15
pubmed:year
1981
pubmed:articleTitle
Spinach Thylakoid Polyphenol Oxidase : ISOLATION, ACTIVATION, AND PROPERTIES OF THE NATIVE CHLOROPLAST ENZYME.
pubmed:affiliation
Martin Marietta Laboratories, 1450 South Rolling Road, Baltimore, MD 21227.
pubmed:publicationType
Journal Article