Kinetic studies of the transphosphorylation reactions catalyzed by alkaline phosphatase from E. coli: hydrolysis of p-nitrophenyl phosphate and o-carboxyphenyl phosphate in presence of Tris.

1. Transphosphorylation of p-nitrophenyl phosphate and o-carboxyphenyl phosphate to Tris, has been studied at alkaline and acid pH. 2. The rate of release for all reactions products was Tris-dependent for both substrates, with a slight maximum for phenol at alkaline pH. These dependences have been analyzed from a mechanistic standpoint. 3. Individual constants of rate of a simple transphosphorylation mechanism have been determined. 4. At high Tris concentration (greater than 1.0 M) a slight competitive inhibition has been observed. 5. Inhibition in NH4+-NH3Cl buffer has been found at alkaline pH but not at acid pH. It would therefore seem that the non-protonated NH2 group of Tris is responsible for inhibition. 6. The results suggest the formation of complexes between Tris and the enzyme. Other possible alternatives are also analyzed.