The Extinction Coefficient of N-Methylated A beta 30-40 Depends on the Position of N-Methylation

The molar extinction coefficient at 210 nm ( epsilon 210) of the N-methylated analogs of A beta 30-40 was analyzed. Additive contributions from a 10-residue peptide main chain ( epsilon 210CONH) and modulation caused by N-methylation ( Delta epsilon 210) accounted for the observed results. The observed epsilon 210CONH value was concordant with reported values. The difference in the Delta epsilon 210 value was explained in terms of changes in electronic structure and conformational restriction resulting from N-methylation.