Changes of Creatine Kinase Secondary Structure Induced by the Release of Nucleotides from Caged Compounds

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Abstract
Light‐induced release of ADP and ATP from their respective caged nucleotides produced small distinct difference infrared spectra of creatine kinase (CK), indicating that ADP and ATP binding to CK promoted different structural alteration. The positive band at 1638–1640 cm−1 and the negative band at about 1650–1652 cm−1 on the reaction‐induced infrared difference spectra in the amide I region were insensitive to the deuteration effects. They were assigned to the peptide backbone of the ADP/ATP‐binding site. In addition Pi or ATP binding produced another positive band at 1657–1659 cm−1 corresponding to the C = O (amide I band) associated with the γ‐phosphate of ATP. This site was also affected when ADP was added, indicating coupling interactions between both sites. No additional structural changes were observed when creatine and ADP were added, suggesting that the creatine‐binding site was uncoupled from the ADP‐binding site. The infrared difference spectra of a transition‐state‐analog complex formed by the addition of ADP, creatine and NO3− (a planar‐phosphate‐mimicking group) lacked the 1657–1659‐cm−1 band indicating that the binding site of γ‐phosphate within CK, was not affected. Infrared changes in the 1560–1590‐cm−1 region suggested that carboxylate groups of Asp or Glu were involved in the binding of Pi, ADP and ATP.

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