The first and rate-limiting enzyme in tetrahydrobiopterin de novo biosynthesis is GTP cyclohydrolase I (GCH1, GTPCHI). Three different isoforms are produced but only isoform 1 is functionally active (Gütlich et al. 1994). GCH1 is functional as a homodecamer. First, a monomer of GCH1 forms a dimer. Then five dimers arrange into a ring-like structure to form the homodecamer (Nar et al. 1995).
Nar, H, Schmid, C, Bacher, A, Weinkauf, S, Meining, W, Huber, R
Rücknagel, KP, Rödl, W, Ziegler, I, Bacher, A, Gütlich, M, Werner, T, Jaeger, E
GTP cyclohydrolase I activity of GCH1 decamer [cytosol]
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