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Catabolic pathway for phenylalanine in plants remains largely elusive since no phenylalanine hydroxylase homolog has been found in higher plants. However, the evidence from feeding experiments with different species of higher plants indicates that phenylalanine is not degraded to any great extent (Mazelis, 1980). It is important to mention that a unique folate-dependent phenylalanine hydroxylase localized in chloroplasts has been identified in non-flowering plants (Pribat et al., 2010). In yeast, first step is performed by either of two aromatic amino acid transaminases. Aromatic amino acid aminotransferase is the main catabolic enzyme, and accepts 2-oxo-3-phenylpropanoate, pyruvate or 4-hydroxyphenylpyruvate, but not 2-oxoglutarate, as the amino acceptor. Reaction utilizing 2-oxoglutarate as the amino acceptor has also been demonstrated, and is likely catalyzed by aromatic amino acid aminotransferase.
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