Figure 41

Three-dimensional drawing of a hemoglobin molecule. Shown are the interrelationship of the two a and two P chains, localization of the helices, amino acids in the chains, and iron molecules in the porphyria structure. Of the aj and P2 chains the helical and nonhelical segments can be identified easily. The individual amino acids are marked as circles and connected to each other. The dark rectangles represent the heme group, and within their center is the iron molecule. These heme groups are localized between the E and F helices. The helices in a hemoglobin molecule are designated by letters from A to H, starting from the amino end. The whole molecule has a spherical form with a three-dimensional measurement of 64 by 55 by 50 Â. (Adapted from Dickerson and Geis [7]; with permission.)

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