Antioxidant Activity of Cysteine and Protein Sulfhydryls in a Linoleate Emulsion Oxidized by Hemoglobin

Fifteen amino acids were evaluated for antioxidant activity in a linoleate emulsion oxidized by hemoglobin. Cysteine was the only amino acid with significant antioxidant activity, which was as great as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), or e‐tocopherol. Ten proteins containing free or latent sulfhydryl groups were evaluated for antioxidant activity in both native and reduced states. Native proteins, containing few or no measurable sulfhydryl groups, had little or no antioxidant activity. Proteins treated with NaBH 4 had greatly increased sulfhydryl groups and antioxidant activity. Treatment of reduced proteins or cysteine with iodoacetic acid (IAA) eliminated both sulfhydryl groups and antioxidant activity. Cysteine and reduced bovine serum albumin had optimum antioxidant activity at pH 8.6.