Kinetics of CheY phosphorylation by small molecule phosphodonors

The chemotaxis response regulator CheY can acquire phosphoryl groups either from its associated autophosphorylating protein kinase, CheA, or from smal l phosphodonor molecules such as acetyl phosphate, We report a stopped-flow kinetic analysis of CheY phosphorylation by acetyl phosphate, The results show that CheY has a very low affinity for this phosphodonor (K-s, much gre ater than 0.1 M), consistent with the conclusion that, whereas CheY provide s catalytic functions for the phosphotransfer reaction, the CheA kinase may act simply to increase the effective phosphodonor concentration at the Che Y active site. (C) 1999 Federation of European Biochemical Societies.