High levels of the end product, BH4, negatively regulates GCH1. It does this via GTP cyclohydrolase 1 feedback regulatory protein (GCHFR). BH4-dependant GCHFR in the form of a homopentamer complexes with the decameric GCH1 enzyme in the ratio 2:1 to inactivate it. L-phenylalanine reverses this inhibition. These regulatory steps control the biosynthesis of BH4. (Swick & Kapatos 2006, Chavan et al. 2006, Harada et al. 1993).
Gillbro, JM, Schallreuter, KU, Rokos, H, Chavan, B
Kagamiyama, H, Hatakeyama, K, Harada, T
Swick, L, Kapatos, G
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