13 C nuclear magnetic resonance study of the CO 2 activation of ribulosebisphosphate carboxylase from Rhodospirillum rubrum

Abstract
Ribulosebisphosphate carboxylase [3-phospho-D-glycerate carboxy-lyase (dimerizing), EC 4.1.1.39] from R. rubrum is activated by CO2 and Mg2+. 13C NMR spectra were determined for the unactivated enzyme and for enzyme that was activated by 13CO2 and Mg2+. Besides the expected resonance for H13CO3-/CO32- at 161.8 ppm downfield from tetramethylsilane, the spectrum of the activated enzyme shows a broad resonance at 164.9 ppm. Analogy with previous NMR studies of 13CO2 binding to Hb, to myoglobin, and to amino acids suggests that the CO2 activation of ribulosebisphosphate carboxylase involves formation of a carbamate between an enzyme amino group and CO2.

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