Abstract
As part of our work to determine the bond properties of the aspartyl phosphate moiety of the Ca^2+^–ATPase (SERCA1a) phosphoenzymes, we analyzed Morse potentials of the bridging PO bond as well as CO bond strengths for the model compound acetyl phosphate and the two phosphoenzyme intermediates Ca~2~E1P and E2P. Reaction‐induced infrared difference spectroscopy was used and a carbonyl band of E2P at 1708 cm^–1^ in the presence of m__M__ Mg^2+^ was tentatively assigned to the carbonyl group of phosphorylated Asp^351^ because of its sensitivity to divalent cations. This band is found at 1716 cm^–1^ with m__M__ Ca^2+^, for Ca~2~E1P at 1717 cm^–1^ with Mg^2+^, and at 1719 cm^–1^ with Ca^2+^ and at 1718 cm^–1^ for acetyl phosphate in the absence of divalent cations. The similar band positions indicate similar strengths of interaction of the carbonyl oxygen in acetyl phosphate and the two phosphoenzymes. Together with information on the PO bond strengths, this implies that the bridging oxygen exerts stronger interactions in the phosphoenzymes than in acetyl phosphate. © 2005 Wiley Periodicals, Inc. Biopolymers 82: 353–357, 2006
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