So in the presence of NADPH and an H plus ion, the enzyme Dihydrophobate reductase basically takes the dihydrobiopterine and transfers the reducing power from NADPH onto this molecule to give us tetrahydrobiopterin. And then this mixed function oxygenates, this enzyme, phenylaline hydroxylase, uses the reducing power of tetrahydrobiopterin to basically form tyrosine. And of course, we also use up the reducing power of this molecule to form Quinnode dihydrobiopterin. Now, to regenerate back the tetrahydrobiopterin so that it can be used again in this reaction, we use an enzyme called dihydropyridine reductase. And this enzyme takes the reducing power of NADPH, transfers it onto this molecule to form back the tetrahydrobiopter. And so that again, we can use the reducing power of this molecule to undergo this first step.