Structural difference in the H+,K+-ATPase between the E1 and E2 conformations - An attenuated total reflection infrared spectroscopy, UV circular dichroism and Raman spectroscopy study

Conformational changes taking place in the gastric H+,K+-ATPase when shifti ng from the K+-induced E2 form to the El form upon replacing K+ ions by Na were investigated by different spectroscopic approaches. No significant se condary-structure change or secondary-structure reorientation with respect to the membrane plane could be measured by attenuated total reflection Four ier transform infrared spectroscopy of oriented films. Circular dichroism a nd Raman spectra obtained on tubulovesicle suspensions indicated no signifi cant secondary structure or tyrosine and tryptophan side-chain environment changes in tubulovesicle suspensions. The smallest observable structural ch anges are discussed in term of the number of amino-acid residues involved f or each technique.