The Presence of Tightly Bound Copper in Ribulose Diphosphate Carboxylase from Spinach

Tightly bound copper has been detected in homogeneous preparations of ribulose 1,5-diphosphate carboxylase purified from spinach. The enzyme has a typical Cu(II) electron paramagnetic resonance spectrum (g ⊥ ∼ g max = 2.09). Analysis by atomic absorption spectrophotometry, electron paramagnetic resonance, and neutron activation indicate the presence of 1 g atom of copper per mole (560,000 g) of carboxylase. The bound copper appears to be present as Cu(II).