Figure 3.

Comparison: Ras·GppNHp on ATR-FTIR and transmission-FTIR. To verify the ATR-FTIR experiments, we performed transmission FTIR experiments with photocaged GppNHp. Bands of α-GppNHp and β-GppNHp were identical, but γ-GppNHp showed two asymmetrical stretching vibrations instead of only one observed vibration in the ATR-FTIR measurements. Isotopic labeling assigned the negative band at 1137 cm⁻¹ to β-GDP. Therefore, the γ-GppNHp band at 1128 cm⁻¹ was superimposed by β-GDP in the ATR-FTIR measurements and reduced to a shoulder. Hence γ-GppNHp owns two asymmetrical stretching vibrations at 1128 cm⁻¹ and 1114 cm⁻¹.