Answer
If phenylalanine is accumulating in a patient's bloodstream:
One should check if the coenzyme for PAH is being properly synthesized.
One should check if the coenzyme for PAH is being properly reduced by NADH, making it available for future reactions.
Work Step by Step
A coenzyme helps an enzyme perform its required functions. If the enzyme PAH is present but is unable to carry out its function, then there must be a deficiency in the coenzyme (as in the case of vitamin C which acts as a coenzyme in the synthesis of collagen).
