Tetrameric protein hemoglobin

John C. Kendrew determined the first atomic-scale (2A resolution) crystallographic structure of a protein, myoglobin (molecular mass 16,900 Da or 16.9 KDa) in 1959 and Max Perutz followed shortly afterward with atomic scale resolution of the tetrameric protein hemoglobin (64,500 Da). The first crystallographic structure for an enzyme, lysozyme (13,900 Da), was determined by David Phillips in 1965. The crystallographic analysis of the structure of the supermolecular photosynthetic reaction center of purple photosynthetic bacteria in 1985 led to a Nobel Prize in chemistry for Robert Huber, Johann Diesenhofer, and Hartmut Michel. The reaction center, a complete nanomachine embedded in the cell membrane of purple photosynthetic bacteria, consists of 4 protein subunits and 14 cofactors. 

The Gd-DOTP chelate (Fig. 18) has been examined as a potential allosteric effector of hemoglobin [113]. Human hemoglobin is a tetrameric protein whose quaternary structure is affected by an allosteric effector. Binding of this low molecular weight species stabilizes the so-called T-form of hemoglobin, which is characterized by a low oxygen affinity, as opposed to the R-form, a very efficient... 

Vertebrate hemoglobins are tetrameric proteins made up of four heme-containing subunits, each capable of binding an 02 molecule. Adult Hbs (a2/b ) consist of two kinds of such subunits (termed a and f ) that in humans are composed of 141 and 146 amino acid residues,... 

From Prob. 1.13, 2,000 hemoglobin molecules are produced per second this is equal to —1.2 x lO per minute. However, hemoglobin is a tetrameric protein (four subunits Chap. 5), so four times 1.2 x 105 chains are produced per minute 4.8 x 105. 

Of particular interest are the developmentally regulated gene families. Similar, but not identical, proteins having the same properties are made at different stages of development. A well-studied example is hemoglobin, a tetrameric protein containing two a subunits and two p subunits. 

Hemoglobin The tetrameric protein in high concentration in red blood cells that binds oxygen in the capillaries of the lungs and delivers it to peripheral tissues. Each globin subunit contains a heme group that binds oxygen when the iron atom is in the ferrous (-1-2) oxidation state. 

Hemoglobin (Hb) is a tetrameric protein composed of two identical alpha subunits and two identical beta subunits. X-ray crystal structures of the low (18) and high (20) affinity states of this protein have been solved at high resolution. 

In many cases there are important interactions between protein molecules that may lead to highly organized structures such as the pleated sheet of silk fibroin (Figure 25-13) or the coiling of a helices, as found in a-keratins, the fibrous proteins of hair, horn, and muscles (Figure 25-17). This sort of organization of protein molecules is called quaternary structure and is an important feature of many proteins that associate into dimers, tetramers, and so on. The tetrameric structure of hemoglobin is an important example. 

---