Table 2. Calculated K_ds and derived ΔG° (Gibbs free energy of binding) for the interactions between eIF4E and the N-Cap derivative peptides.

Peptide	Sequence	SPR derived Kd (nM)		(ΔG°, cal mol−1)
		Keq	Kkin	Keq derived	Kkin derived
eIF4G1	1KKRYDREFLLGF12	580.2±16.7	523.9±61.6	−8500±20	−8550±70
eIF4E-D5S	1KKRYSREFLLGF12	103.0±2.3	99.9±6.2	−9520±10	−9540±40
eIF4E-D5T	1KKRYTREFLLGF12	110.2±1.8	104.9±7.2	−9480±10	−9510±40
eIF4E-D5G	1KKRYGREFLLGF12	467.8±28.1	439.5±26.0	−8630±40	−8660±40
eIF4E-D5P	1KKRYPREFLLGF12	683.7±13.6	717.3±31.2	−8400±10	−8370±100
eIF4E-D5N	1KKRYNREFLLGF12	444.5±1.6	388.9±1.6	−8660±10	−8740±10
eIF4E-D5E	1KKRYEREFLLGF12	749.0±57.7	692.4±31.2	−8350±50	−8390±30
eIF4E-D5C	1KKRYCREFLLGF12	436.5±6.4	458.0±19.8	−8670±10	−8640±30

The table shows the peptide sequences used to study the influence of alternative residues and their effects in capping the first turn of the α-helix when bound to eIF4E. K_ds were determined using SPR with eIF4E immobilized on the chip surface. K_ds were derived from the equilibrium responses (K_eq) and from the association and dissociation phases (K_kin) of the SPR data. The Gibbs free energy of binding (ΔG°) was calculated with the equation ΔG = –RT ln K_a using both dissociation constant values determined.