Protein oxidation: examination of potential lipid-independent mechanisms for protein carbonyl formation

✍ Scribed by D. P. Blakeman; T. P. Ryan; R. A. Jolly; T. W. Petry

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 114 KB
• Volume: 12
• Category: Article
• ISSN: 1095-6670
• DOI: 10.1002/(sici)1099-0461(1998)12:3<185::aid-jbt7>3.0.co;2-h

✦ Synopsis

Previous data indicated that diquat-mediated protein oxidation (protein carbonyl formation) occurs through multiple pathways, one of which is lipid dependent, and the other, lipid independent. Studies reported here investigated potential mechanisms of the lipid-independent pathway in greater detail, using bovine serum albumin as the target protein.

One hypothesized mechanism of protein carbonyl formation involved diquat-dependent production of H 2 O 2 , which would then react with site-specifically bound ferrous iron as proposed by Stadtman and colleagues. This hypothesis was supported by the inhibitory effect of catalase on diquat-mediated protein carbonyl formation. However, exogenous H 2 O 2 alone did not induce protein carbonyl formation. Hydroxyl radical-generating reactions may result from the H 2 O 2 -catalyzed oxidation of ferrous iron, which normally is bound to protein in the ferric state. Therefore, the possible reduction of site-specifically bound Fe ‫3‬ to Fe ‫2‬ by the diquat cation radical (which could then react with H 2 O 2 ) was also investigated. The combination of H 2 O 2 and an iron reductant, ascorbate, however, also failed to induce significant protein carbonyl formation. In a phospholipid-containing system, an ADP:Fe ‫2‬ complex induced both lipid peroxidation and protein carbonyl formation; both indices were largely inhibitable by antioxidants. There was no substantial ADP:Fe ‫2‬ -dependent protein carbonyl formation in the absence of phospholipid under otherwise identical conditions. Based on the lipid requirement and antioxidant sensitivity, these data suggest that ADP:Fe ‫2‬dependent protein carbonyl formation occurs through reaction of BSA with aldehydic lipid peroxidation products. The precise mechanism of diquat-mediated