Subunits of the Extracellular Hemoglobin of Arenicola Marina
Kosinski, Timothy Frank
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The molecular weight of the extracellular hemoglobin of Arenicola marina determined by equilibrium sedimentation is 3.74 ± 12 X 10^6, which corresponds to 163 ±12 iron atoms per molecule. Its iron content is 0.244 ± 0.005 wt. %corresponding to an average molecular lfetight of 22.900 ± 500 for the polypeptide chains in each of the twelve spherical subunits which make up the hemoglobin of Arenicola. Polyacrylamide gel electrophoresis in sodium dodecyl sulfate showed that the hemoglobin dissociated into three distinct polypeptide subunits: 14,000 molecular weight (subunit 1), 31,000 (subunit 2) and 49,000 (SUbunit 3). In the presence of 2-mercaptoethanol four subunits were observed, 14,000 (subunit I), 16,000 (subunit II), 31,000 (subunit III), and 35,000 (subunit IV). Two-dimensional electrophoresis in mercaptoethanol showed that subunit 1 produced subunit I, and subunits 2 and 3 produce subunits I, II and variable amounts of subunits III and IV. The dissociation products from subunits 1, 2 and 3 may be the result of intra and interspecific disulfide bond breakage in the polypeptide chains. Gel filtration of reduced and alkylated Arenicola marina hemoglobin in 6 M guanidinium hydrochloride suggests that the molecular weight of subunits I and II is 17,500 ± 1,000, and subunits III and IV may be polymers of this monomer. Therefore it is proposed that some of the polypeptide chains can associate to form dimers, such as subunit 2, III and IV, or trimors as in subunit 3. We report below the results of our studies of the subunit structure of Arenicola marina hemoglobin.