Related Experiment Videos
Peroxidase/hydrogen peroxide--or bone marrow homogenate/hydrogen peroxide--mediated activation of phenol and binding
V V Subrahmanyam1, L G McGirr, P J O'Brien
1Faculty of Pharmacy, University of Toronto, Ontario, Canada.
Abstract:
1. 14C-Phenol was metabolized by rat bone marrow homogenate and H2O2. The homogenate catalyst, however, was inactivated by preincubation with H2O2, presumably due to inactivation of the enzyme(s) involved in phenol metabolism. 2. The majority of the metabolized 14C-phenol was bound to bone marrow proteins. o,o'-Biphenol and p,p'-biphenol were the principal non-protein-bound products. Ascorbate was unable to remove phenol oxidation products bound to protein, although o,o'-biphenol recovery from the reaction mixture was markedly enhanced. Prior alkylation of protein thiols with N-ethylmaleimide decreased the binding of 14C-phenol oxidation products to bone marrow proteins by only 10-20%. 3. 14C-Phenol (200 microM) metabolism by horseradish peroxidase (10 micrograms) and H2O2 (200 microM) also resulted in extensive binding to externally added bovine serum albumin. The absorption spectrum of 14C-phenol oxidation products bound to bovine serum albumin was similar to that of bound oxidation products of o,o'-biphenol but not of p,p'-biphenol. 4. Protease digestion of bovine serum albumin bound 14C-phenol oxidation products, followed by ethyl acetate extraction, extracted 75% of the 14C, indicating that most of the binding is probably non-covalent. Up to 32% of the 14C-phenol oxidation products binding to bovine serum albumin may be covalent, since derivation with dinitrofluorobenzene and extraction under acid, but not alkaline, conditions extracted the 14C. The percentage of metabolites covalently bound to bovine serum albumin was increased to 59% when horseradish peroxidase concentration was decreased to 0.2 micrograms. 5. The thiol groups of bovine serum albumin were unaffected by o,o'-biphenol oxidation products, slightly decreased by phenol oxidation products, but were completely depleted by p,p'-biphenol oxidation products. 6. These results indicate that o,o'-biphenol oxidation products are responsible for much of the 14C-phenol binding to protein.