Differences in Susceptibility Between Crystallins and Non-Lenticular Proteins to Copper and H₂O₂-Mediated Peptide Bond Cleavage

Abstract

The relative susceptibilities of lenticular proteins (α, β and γ-crystallins) and a number of proteins of non-lenticular origin, to hydroxyl radical-mediated peptide bond cleavage were compared. The non-lenticular proteins (bovine serum albumin, ovalbumin, alcohol dehydrogenase, lysozyme, thyroglobulin, β-amylase, haemoglobin and carbonic anhydrase) were readily cleaved into acid-soluble fragments following 5 hours treatment with copper ions and hydrogen peroxide. In contrast the crystallins were almost totally unaffected by similar treatment. When α-crystallin was pre-treated with acid or cleaved into large fragments with cyanogen bromide it became susceptible to hydroxyl radical attack, yet heating the protein did not diminish its resistance. It is suggested that the resistance of α-crystallin to the copper/peroxide-mediated fragmentation may be dependent on the conformation of the protein.

Key Words:

• Oxygen free radicals
• crystallin
• polypeptide fragmentation