Binds to and modulates the activity of GTP cyclohydrolase I. GTP cyclohydrolase I activity catalyzes the reaction: GTP + 2 H2O = formate + 2-amino-4-hydroxy-6-(erythro-1,2,3-trihydroxypropyl)-dihydropteridine triphosphate.
GTP cyclohydrolase I regulator activity