Facilitation of the Terminal Proton Transfer Reaction of Ribulose 1,5-Bisphosphate Carboxylase/Oxygenase by Active-Site Lys166†

The terminal step in the carboxylation pathway catalyzed by ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) is stereospecific protonation of the C-2 aci-acid of 3-phosphoglycerate (PGA). X-ray crystallographic results favor the e-amino group of Lys166 as the proton donor in this step [Knight et al. (1990) J. Mol. Biol. 215, 113]. Nonetheless, position-166 mutants are able to catalyze forward processing of isolated 2-carboxy-3-ketoarabinitol 1,5-bisphosphate (CKABP), the carboxylated reaction intermediate [Lorimer, G. H., & Hartman, F. C. (1988) J. Biol. Chem. 263, 6468]. Prior assays for intermediate processing relied solely on formation of acid-stable radioactivity from acid-labile [2‘-14C]CKABP. Therefore, PGA, the normal reaction product, may not have been distinguished from pyruvate, the product from β-elimination of phosphate from the terminal aci-acid intermediate [Andrews, T. J., & Kane, H. J. (1991) J. Biol. Chem. 266, 9447]. If Lys166 indeed serves as the terminal proton donor, mutants ...