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Sapropterin, also known as tetrahydrobiopterin (BH4), is a naturally occurring enzyme cofactor that plays a crucial role in the metabolism of phenylalanine (Phe) in the human body [1]. Phenylalanine is an essential amino acid, meaning it cannot be produced by the body and must be obtained through diet. However, excessive levels of Phe can be toxic and lead to neurological issues, as seen in phenylketonuria (PKU), a genetic disorder that affects Phe metabolism [1].

Sapropterin regulates phenylalanine levels by facilitating the conversion of Phe to tyrosine, another amino acid, through the action of the enzyme phenylalanine hydroxylase (PAH) [1]. In PKU patients, PAH function is impaired, leading to an accumulation of Phe and its toxic byproducts [1]. By providing an external source of sapropterin, PAH function can be partially restored, thereby reducing Phe levels and alleviating some of the symptoms associated with PKU [1].

It is important to note that sapropterin treatment is most effective in PKU patients with some residual PAH activity [1]. Additionally, sapropterin treatment must be combined with a Phe-restricted diet for optimal results [1].

In summary, sapropterin regulates phenylalanine levels by facilitating the conversion of Phe to tyrosine through the action of PAH. This process is particularly important in PKU patients, where PAH function is impaired, leading to an accumulation of Phe and its toxic byproducts. Sapropterin treatment can help restore PAH function and reduce Phe levels in PKU patients, but it is most effective in those with some residual PAH activity and must be used in conjunction with a Phe-restricted diet.

Sources:
[1] DrugPatentWatch.com - Sapropterin: <https://www.drugpatentwatch.com/drugs/sapropterin>