THE AMOUNT OF ULTRAVIOLET ABSORBENCY IN A SYNTHETIC PEPTIDE IS DIRECTLY PROPORTIONAL TO ITS NUMBER OF PEPTIDE-BONDS

The UV absorption at 200 nm of eleven synthetic peptides, all lacking an aromatic amino acid side chain, was studied. Those peptides were Ala(2), Ala(3), Ala(4), Ala(5), Ala(6) . HCl, Gly(2), Gly(3), Gly(4), Gly(5), SIGSLAK, and PLSRTLSVAAKK. It was determined, using the rapid analysis time and high sensitivity of capillary zone electrophoresis (CZE), that the amount of UV light absorbed by each peptide was directly related to the number of peptide bonds. This relationship held true, not only for the Ala- and Gly-containing oligopeptides, but also for the bioactive peptides SIGSLAK (active site peptide of penicillin-binding protein 1b from E. coli) and PLSRTLSVAAKK (Protein Kinase C substrate). Those analytical techniques that use UV detection for peptides, such as high performance liquid chromatography (HPLC) and CZE, will likely observe the same relationship between absorbance and the number of peptide bonds within a peptide, barring any effect on UV absorbance due to UV-absorbing aromatic side chains or the existence of secondary structure that might alter UV absorption. The findings of this study also provide an explanation for the lower detection limits (higher sensitivity) seen throughout the literature for proteins as compared to peptides; namely, proteins, with their greater number of peptide bonds, inherently absorb more UV light, proportionally improving the limit of their detection.