The glycerate kinase of a serine-producing methylotroph, Hyphomicrobium methylovorum GM2, was purified to complete homogeneity and characterized, the first time for an enzyme from a methylotroph. The enzyme was a monomer with a molecular mass about 41-52 kDa. The enzyme was stable against heating at 35 degrees C for 30 min at pH values over 6-10. Maximum activity was observed at pH 8.0 and around 50 degrees C. The Km values for D-glycerate and ATP were 0.13 mM and 0.13 mM, respectively. The enzyme showed high specificity for D-glycerate, and was activated by potassium and ammonium ions. The reaction product of the enzyme was identified as 2-phosphoglycerate.