Document Detail

Latent and active polyphenol oxidase (PPO) in red clover (Trifolium pratense) and use of a low PPO mutant to study the role of PPO in proteolysis reduction.
MedLine Citation:
PMID:  18361497     Owner:  NLM     Status:  MEDLINE    
Polyphenol oxidase (PPO) activity in leaf extracts of wild type (WT) red clover and a mutant line expressing greatly reduced levels of PPO (LP red clover) has been characterized. Both latent and active forms of PPO were present, with the latent being the predominant form. PPO enzyme and substrate (phaselic acid) levels fluctuated over a growing season and were not correlated. Protease activation of latent PPO was demonstrated; however, the rate was too low to have an immediate effect following extraction. A novel, more rapid PPO activation mechanism by the enzyme's own substrate was identified. Rates of protein breakdown and amino acid release were significantly higher in LP red clover extracts compared with WT extracts, with 20 versus 6% breakdown of total protein and 1.9 versus 0.4 mg/g FW of free amino acids released over 24 h, respectively. Inclusion of ascorbic acid increased the extent of protein breakdown. Free phenol content decreased during a 24 h incubation of WT red clover extracts, whereas protein-bound phenol increased and high molecular weight protein species were formed. Inhibition of proteolysis occurred during wilting and ensilage of WT compared with LP forage (1.9 vs 5 and 17 vs 21 g/kg of DM free amino acids for 24 h wilted forage and 90 day silage, respectively). This study shows that whereas constitutive red clover PPO occurs predominantly in the latent form, this fraction can contribute to reducing protein breakdown in crude extracts and during ensilage.
Ana L Winters; Frank R Minchin; Terry P T Michaelson-Yeates; Michael R F Lee; Phillip Morris
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Publication Detail:
Type:  Journal Article     Date:  2008-03-25
Journal Detail:
Title:  Journal of agricultural and food chemistry     Volume:  56     ISSN:  0021-8561     ISO Abbreviation:  J. Agric. Food Chem.     Publication Date:  2008 Apr 
Date Detail:
Created Date:  2008-04-17     Completed Date:  2008-07-09     Revised Date:  2014-10-14    
Medline Journal Info:
Nlm Unique ID:  0374755     Medline TA:  J Agric Food Chem     Country:  United States    
Other Details:
Languages:  eng     Pagination:  2817-24     Citation Subset:  IM    
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MeSH Terms
Amino Acids / metabolism
Ascorbic Acid / pharmacology
Caffeic Acids / analysis,  metabolism
Catechol Oxidase / analysis,  genetics*,  metabolism*
Enzyme Activation
Malates / analysis,  metabolism
Peptide Hydrolases / metabolism
Phenols / analysis
Plant Leaves / enzymology*
Trifolium / enzymology*,  growth & development
Grant Support
BBS/E/W/00003134D//Biotechnology and Biological Sciences Research Council
Reg. No./Substance:
0/Amino Acids; 0/Caffeic Acids; 0/Malates; 0/Phenols; 0/phaselic acid; EC Oxidase; EC 3.4.-/Peptide Hydrolases; PQ6CK8PD0R/Ascorbic Acid

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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