What is sapropterin's function in creating cofactors?

Sapropterin is a synthetic form of tetrahydrobiopterin (BH4). BH4 is a crucial cofactor for several enzymes, especially:

- Phenylalanine hydroxylase (PAH), which converts phenylalanine to tyrosine.
- Tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH), which synthesize neurotransmitters (dopamine/ norepinephrine and serotonin, respectively).

By supplying BH4, sapropterin replenishes this cofactor pool, increasing PAH activity and lowering blood phenylalanine levels in people with BH4-responsive phenylketonuria (PKU). It also supports downstream neurotransmitter synthesis through TH and TPH. It’s not itself creating new cofactors from scratch; it provides the BH4 cofactor that the enzymes need.