Purification and Characterization of Guanosine Triphosphate Cyclohydrolase from Serratia indica

Abstract

Multipe forms (D-I and D-II) of GTP cylcohydrolase, the first enzyme in pteridine biosynthesis, was demonstrated in Serratia indica by DEAE-cellulose chromatography. D-II was purified homogeneously. D-I contained small amounts of inactive protein. Both molecular weights were estimated to be 200,000. D-II consisted of 8 subunits with the same molecular weight of 25,000. The Km values (Km₁ and Km₂) for GTP were 3.2 µm and 0.61 µm for D-I, and 0.44 µm and 5.5 µm for D-II, respectively. Bivalent cations (Cu²⁺, Cd²⁺, Hg²⁺) inhibited the enzymes. Univalent cations (K⁺, Na⁺ and Li⁺) activated the enzymes.