RGP	radial growth phase
VGP	vertical growth phase
NOS	nitric oxide synthase
NO	nitric oxide
ROS	reactive oxygen species
BH4	tetrahydrobiopterin
BH2	dihydrobiopterin
GTPCH1	GTP cyclohydrolase protein
GCH1	murine cyclohydrolase gene
PTPS	6-pyruvoyltetrahydrobiopterin synthase protein
SR	sepiapterin reductase protein
GFRP	GTP feedback regulator protein
GCHFR	human GTP feedback regulator gene
DHFR	dihydrofolate reductase
DHPR	dihydropteridine reductase