Tyrosine decarboxylase

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Abstract
We have developed a highly sensitive and rapid spectrophotometric assay for tyrosine decarboxylase that can be applied to determining pyridoxal-5′-phosphate. In the assay, tyramine, a product of tyrosine decarboxylation, reacts with 2,4,6-trinitrobenzenesulfonic acid to give a product soluble in toluene whereas tyrosine does not. We determined the amount of tyramine produced enzymatically by reading the absorbance at 340 nm of a toluene extract of the reaction mixture. This method is capable of detecting as low as 2.9 μg/mL of the enzyme. Using this method, we find theK m for tyrosine decarboxylase fromStreptococcus faecalis to be 3.55×10−4 M. We have also developed a specific and extremely sensitive method for determining pyridoxal-5′-phosphate, a cofactor of the enzyme, by using this spectrophotometric assay with apotyrosine decarboxylase.

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