Proteolytic stability of β-peptide bonds probed using quenched fluorescent substrates incorporating a hemoglobin cleavage site

A set of designed internally quenched fluorescence peptide substrates has been used to probe the effects of insertion of β-peptide bonds into peptide sequences. The test sequence chosen corresponds to a proteolytically susceptible site in hemoglobin β-chain, residues 32-37. Fluorescence and mass spectral measurements demonstrate that the insertion of an α-residues at the potential cleavage sites completely abolishes the action of proteases; in addition, the rate of cleavage of the peptide bond preceding the site of modification is also considerably reduced