Mechanisms for the ring conversion of GTP into cofactor precursors by
GTP cyclohydrolases and molybdopterin synthase are proposed and discus
sed in the context of the crystal structure of the GTP cyclohydrolase
I-2'-deoxy-GTP complex. The mechanisms suggest that common features of
acid-base catalysis may underly the reactions catalysed in all three
cases. (C) 1997 Elsevier Science Ltd.