Reactivity of human leukocyte elastase and porcine pancreatic elastase toward peptide 4-nitroanilides containing model desmosine residues. Evidence that human leukocyte elastase is selective for cross-linked regions of elastin.

Elastin contains a number of cross-linking amino acid residues such as desmosine and isodesmosine which are primarily hydrophobic in character, but have a positively charged pyridinium ring. These cross-linking residues are formed by the action of lysyl oxidase upon Lys residues in tropoelastin, a precursor of elastin. A series of tetrapeptide 4-nitroanilides which contain Lys and a series of modified lysine residues were synthesized. The modified lysine residues [epsilon-carbobenzyloxy (Z), epsilon-benzoyl (Bz), epsilon-benzimidoyl (Bim), and epsilon-2-picolinoyl (Pic)] have various characteristics of desmosine and isodesmosine residues, such as a positive charge, a hydrophobic aromatic ring, or a pyridine ring. The reactivity of the tetrapeptide 4-nitroanilides containing the model desmosine residues at P4, P3, or P2 with human leukocyte (HL) and porcine pancreatic (PP) elastase was measured at pH 7.5 and 25 degrees C. HL elastase exhibited high reactivity toward the substrates with P4 or P3 hydrophobic groups (Z, Bz, or Pic), and MeO-Suc-Lys(Pic)-Ala-Pro-Val-NA is 7 times more reactive than the previous best HL elastase substrate, MeO-Suc-Ala-Ala-Pro-Val-NA. The major change occurred in KM values. The substrates containing Lys residues were either nonreactive or poor. Except for two substrates with P2 hydrophobic residues (Bz and Pic), PP elastase was less reactive toward the substrates containing model desmosine residues than toward MeO-Suc-Ala-Ala-Pro-Val-NA. The data support the hypothesis that HL elastase cleaves elastin selectively ner cross-linking residues. The results also indicate that HL elastase binds tightly to these regions and would be poorly effective toward regions of elastin or tropoelastin which contain Lys residues.