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A monophenol oxidase activity in extracts of sorghum.
MedLine Citation:
PMID:  16657306     Owner:  NLM     Status:  PubMed-not-MEDLINE    
A p-hydroxycinnamic acid oxidase activity was present in enzyme preparations from first internodes of Sorghum vulgare variety Wheatland milo when incubated in phosphate buffer at pH 7.5. This preparation had no classical polyphenolase activity but had both peroxidase and catalase activities. Since horseradish preparations catalyzed the same reaction, the oxidation probably is another example of a peroxidase-oxidase reaction. A second substrate was p-hydroxyphenylpyruvic acid. Ferulic acid was slightly active at low concentrations and inhibitory at higher ones. Diphenols such as caffeic and chlorogenic acids were inactive and inhibitory to p-hydroxycinnamic acid oxidation. A variety of monophenols such as tyrosine and cinnamic acid were inactive. An active substrate must have a free monophenolic group and para to this a C(3) side chain with a double bond and probably a free terminal acid group. A sulfhydryl reducing agent at the 5 millimolar level such as mercaptoethanol, reduced glutathione, or dithiothreitol was obligatory. Products were varied and were found in both the ethyl acetate-soluble and insoluble fractions after acidification of the incubation mixtures. With internode extracts, about 1 micromole of O(2) was consumed per micromole of p-hydroxycinnamic acid that disappeared in the presence of mercaptoethanol. Tetrahydrafolic acid plus mercaptoethanol were required for a second step oxidation or a parallel reaction; about 2 micromoles of O(2) were consumed per micromole of p-hydroxycinnamic acid that disappeared. Potassium cyanide, diethyldithiocarbamate, ascorbic acid, and ethylenediaminetetraacetate were inhibitory. A similar mercaptoethanol-dependent monophenol oxidase was present in preparations from green shoots that also contained a classical polyphenolase activity. The activity was present in both soluble and particulate (500 to 100,000 gravity) fractions of internodes. Preliminary studies were made of enzyme complexes in the particulate fractions capable of converting phenylalanine and tyrosine to the level of ferulic acid when the above p-hydroxycinnamic acid oxidase was blocked with ascorbic acid. The ratelimiting step was the hydroxylation of p-hydroxycinnamic acid.
H A Stafford; R Baldy
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Plant physiology     Volume:  45     ISSN:  0032-0889     ISO Abbreviation:  Plant Physiol.     Publication Date:  1970 Feb 
Date Detail:
Created Date:  2010-06-29     Completed Date:  2010-06-29     Revised Date:  2010-09-14    
Medline Journal Info:
Nlm Unique ID:  0401224     Medline TA:  Plant Physiol     Country:  United States    
Other Details:
Languages:  eng     Pagination:  215-22     Citation Subset:  -    
Biology Department, Reed College, Portland, Oregon 97202.
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