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N Biotechnol. 2010 Sep 30;27(4):308-16. doi: 10.1016/j.nbt.2010.04.003. Epub 2010 Apr 18.

PCR amplification and cloning of tyrosine decarboxylase involved in synephrine biosynthesis in Citrus.

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Western Regional Research Center, Agricultural Research Service, United States Department of Agriculture, 800 Buchanan St., Albany, CA 94710, USA.



The phenolic amine synephrine is a vascoconstrictor and bronchiectatic agent and holds promise as an aid to weight management and obesity reduction. Synephrine is structurally similar to the active ingredients of several commercial cold remedies. Some Citrus contain high concentrations of synephrine. An enzyme involved in synephrine biosynthesis, tyrosine decarboxylase (TYDC), is a pyridoxal-5'-phosphate (PLP)-dependent enzyme that decarboxylates tyrosine to yield CO(2) and tyramine. We used PCR to screen, clone and sequence this gene from various synephrine producing and nonproducing Citrus species and varieties to determine if DNA sequence of this gene correlated with synephrine presence.


PCR amplification and comparison of DNA sequence indicates DNA sequence differences that may cause production of truncated proteins to be produced in some nonsynephrine producing Citrus.


Synephrine production may be genetically determined in part by the gene for TYDC.

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