Inhibition by thiols of copper(II)-induced oxidation of oxyhemoglobin.
The ability of thiols, 2-imidazolethiones and uric acid to protect bovine oxyhemoglobin from copper(II)-induced oxidation to methemoglobin was investigated. The oxidation of oxyhemoglobin by Cu(II) proceeded in two phases: (1) an initial rapid reaction (less than 30 s) followed by (2) a slower reaction that carried it to completion. Thiols, including N-acetyl-L-cysteine, DL-dithiothreitol, reduced glutathione, DL-homocysteine, 2-mercaptoethanol and 2- and 3-mercaptopropionic acid, whose sulfhydryl groups were slowly oxidized by Cu(II) (with the exception of 2-mercaptopropionic acid), protected oxyhemoglobin in both phases of the reaction. Other thiols, including L-cysteine, cysteamine, and D-penicillamine, whose sulfhydryl groups were readily oxidized by Cu(II), protected hemoglobin initially, but within 2-4 min, the rate of methemoglobin formation was the same as Cu(II)-treated oxyhemoglobin. 2-Mercaptoimidazole and 1-methyl-2-mercaptoimidazole, which complex Cu(II) and inhibit Cu(II)-catalyzed oxidation of ascorbic acid, also protected hemoglobin in the initial phase, but not in the second phase. Uric acid, L-ergothioneine, and thiourea did not protect oxyhemoglobin in either the fast or slow phase. Cu(II) may have a coordination site involved in the oxidation of hemoglobin that is not blocked by the 2-imidazolethiones, uric acid, or the oxidized thiols. It is concluded that certain thiols that complex Cu(II) and are not rapidly oxidized will protect oxyhemoglobin from Cu(II)-induced oxidation, but the thiols are no longer effective once they are oxidized.
Smith
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RC
Department of Animal and Dairy Sciences, Auburn University, Alabama 36849-5415.
Reed
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VD
D000818:Animals; D000975:Antioxidants; D002417:Cattle; D003300:Copper / Q000097:blood / Q000494:pharmacology*; D019327:Copper Sulfate; D008706:Methemoglobin / Q000378:metabolism; D010084:Oxidation-Reduction / Q000187:drug effects; D010108:Oxyhemoglobins / Q000187:drug effects* / Q000378:metabolism; D010396:Penicillamine / Q000494:pharmacology; D013438:Sulfhydryl Compounds / Q000097:blood / Q000494:pharmacology*; D014527:Uric Acid / Q000097:blood / Q000494:pharmacology
D000975:Antioxidants; D010108:Oxyhemoglobins; D013438:Sulfhydryl Compounds; D014527:Uric Acid; D003300:Copper; D008706:Methemoglobin; D010396:Penicillamine; D019327:Copper Sulfate