The molecular architecture of the extracellular hemoglobin of Ophelia bicornis : analysis of individual molecules

Abstract The dimensions and shape of extracellular hemoglobin molecules of the marine worm, Ophelia bicornis , were determined by electron microscopy using negative staining and embedding in aurothioglucose. The typical averaged double-layered hexagon has a diameter of 26.5 nm and a height of 18 nm. The three-dimensional reconstruction of the negatively stained samples, using random conical tilting, showed about 60% of the original height of the molecule due to flattening and incomplete embedding in stain. In contrast to this, the specimen embedded in aurothioglucose showed no flattening. The three-dimensional reconstructions agree with the structure found in a previous study on 2-D crystalline arrays. In particular, the main subunit shows more than three mass centers.