The respiratory protein, erythrocruorin, of the annelid Arenicola marina was investigated. Spectral properties show many analogies with those of vertebrate hemoglobine. 144 heme groups (ferroprotoporphyrin) were found in the whole molecule, which has a relative molecular mass of 3.56 x lo6, as determined by sedimentation equilibrium, and an isoelectric point of 4.69. Protein dissociation patterns were analysed by electrophoresis after denaturation in the presence of dodecylsulfate, with and without 2-mercaptoethanol. A tentative model associating molecular mass of the native molecule, heme content, molecular mass of the polypeptide chains and functional properties is proposed. A twelfth subunit of A . marina erythrocruorin would contain twelve heme groups arranged in three functional units made up of four protomers, half of these being covalently bound to non-heme chains; two structural chains would be spatially arranged as bonds between the subunits.
The intertidal lugworm, Arenicola marina, develops a respiratory and metabolic blood acidosis when the oxygen availability is reduced during emersion time at low tide. Measurement of volatile fatty acids in prebranchial blood sampled in the field showed that blood acetate and propionate concentrations increased with length of emersion time. Experimentally confined lugworms excreted acid by-products into the medium when water oxygen tension dropped below 50 Torr (1 Torr = 133.322 Pa) or when oxyhemoglobin concentration fell below 0.45 mmol L−1. A metabolism oriented toward easily excreted end-products may be considered as adaptive in view of the energy yield and the possibility of minimizing metabolic acidosis.
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