Interference by a Phenylacetate Pathway in Isotopic Assays for Phenylalanine Ammonia-Lyase in Leaf Extracts

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Abstract
Particulate and soluble fractions from leaves of Sorghum, Spinacia (spinach), and Coleus, capable of metabolizing l-phenylalanine to cinnamate or to caffeate, are also able to convert l-and d-phenylalanine to phenylacetate. Since cinnamate and phenylacetate are not effectively separated in commonly used chromatographic solvents, some of the isotropic assays used for phenylalanine ammonia-lyase are rendered ambiguous by the interference of this second pathway. Therefore, a “double decker,” two-dimensional paper chromatographic method was designed to separate cinnamate and phenylacetate. This was combined with the use of phenylalanine labeled randomly or just in either the carbon 1 or 2 position of the side chain.