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Abstract
Large, multimeric heme proteins are currently being used as models for therapeutic oxygen carriers (the major function of “artificial blood”). Accurate measurements of formal reduction potentials for hemoglobin related oxygen carriers are crucial since oxidation of heme‐iron results in loss of oxygen binding. To investigate possible structure‐function differences between intracellular and extracellular oxygen transport proteins, the formal reduction potential for a series of oxygen binding proteins was determined. Monomeric horse heart myoglobin (Mb), tetrameric normal adult human hemoglobin (HbA), tetrameric human sickle cell hemoglobin (HbS), polymeric Lumbricus terrestris hemoglobin (LtHb), and polymeric Callinectes sapidus hemocyanin (Hc) were investigated using absorption spectroelectrochemistry with mediated electron transfer. Data were evaluated using Nernst plots and yielded the following E°′ results: +73 (±5) mV for LtHb, −50 (±8) mV for HbA, −52 (±7) mV for HbS, −100 (±25) mV for Hc, and −157 (±5) mV for Mb. All errors represent one standard deviation. Potentials measured relative to Ag/AgCl.