When levels of phenylalanine rise too high in the body, and the main metabolic route is blocked, secondary reactions come to the fore. The immediate consequence of a blockage in the hydroxylation of phenylalanine is that levels of phenylpyruvate start to rise. Phenylpyruvate derives from phenylalanine through a simple transamination reaction:
Subsequently, there is further metabolism of the phenylpyruvate.
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