Hemoglobin subunit selectivity

Chemical perturbations can be a useful approach to this problem. In laccase, selective replacement of the type 1 coppo- with mercury has allowed the type 1 site in laccase to be characterized stmcturally, even in the presence of three other copper atoms (27). Likewise, Simolo et al. have studied independently the a and 3 subunits in hemoglobin by preparation of the (a-M)2(P-M )2 derivaties, where M and M are different metals (28). An alternative to replacement is metal removal, for example Cu in cytochrome-c oxidase (29) or the T3 Ci in laccase (30). The concern with all of these approaches is to establish that the modified protein has the same metal-site structures as the native protein. 

Figure 4.13 Anatomy of selected proteins. (A) The /3 subunit of hemoglobin carrying a heme molecule (B) triose isomerase and (C) /3-lactoglobulin carrying a molecule of vitamin A. Spirals represent helix segments, and the broad arrows are pleated sheet polypeptide segments showing the direction from the N to the C terminus. (A and B reproduced with permission from Richardson JS. The anatomy and taxonomy of protein structure. Adv Prot Chem 34 168-339, 1981. C reproduced with permission from Papiz MZ, Sawyer L, Eliopoulos EE, North ACT, Findlay JBC, Sivaprasadarao R, Jones TA, Newcomer ME, Kraulis PJ. The structure of beta-lactoglobulin and its similarity to plasma retinol-binding protein. Nature 324 383-385, 1986.)...

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