Fig. 1.

(a) The propionate-to-succinate pathway, propionyl-CoA carboxylase (PCC), 5′-deoxyadenosylcobalamin (AdoCbl); (b) metabolism of the BH4 cofactor, GTP cyclohydrolase I (GCH1), dihydropteridine reductase (DHPR), 6-pyruvoyl tetrahydropterin synthase (PTPS), pterin 4α-carbinolamine dehydratase (PCD), phenylalanine hydroxylase (PAH), tyrosine hydroxylase (TH), tryptophan hydroxylase (TPH); (c) localization of the SR and MCEE genes on chromosome 2. The hatched line represents a non-enzymatic step or an unknown shunt pathway