Dissociated active subunits of tobacco phosphodiesterase

The tetrameric nature of the phosphodiesterase isolated from tobacco cells is confirmed by determining the number of oligomers formed upon cross-linking the enzyme with dimethyl suberimidate. The isolation of the catalytically active monomer, which is formed by incubating the enzyme with urea and 2-mercaptoethanol, has been accomplished by gel filtration on Sephadex G-200. The isolated monomer of the phosphodiesterase is stable under nondenaturing conditions and catalytically active. The enzyme activity of the phosphodiesterase monomer is more sensitive to SDS than the tetramer. The phosphodiesterase tetramer exhibits characteristics of negative cooperativity, while the isolated monomer does not.