Hemoglobin monomeric

The terms polypeptide and protein are used interchangeably in discussing single polypeptide chains. The term protein broadly defines molecules composed of one or more polypeptide chains. Proteins having only one polypeptide chain are monomeric proteins. Proteins composed of more than one polypeptide chain are multimeric proteins. Multimeric proteins may contain only one kind of polypeptide, in which case they are homomultimeric, or they may be composed of several different kinds of polypeptide chains, in which instance they are heteromultimeric. Greek letters and subscripts are used to denote the polypeptide composition of multimeric proteins. Thus, an ag type protein is a dimer of identical polypeptide subunits, or a homodimer. Hemoglobin (Table 5.1) consists of four polypeptides of two different kinds it is an hetero-multimer. 

The properties of individual hemoglobins are consequences of their quaternary as well as of their secondary and tertiary structures. The quaternary structure of hemoglobin confers striking additional properties, absent from monomeric myoglobin, which adapts it to its unique biologic roles. The allosteric (Gk alios other, steros space ) properties of hemoglobin provide, in addition, a model for understanding other allosteric proteins (see Chapter 11). 

Myoglobin is monomeric hemoglobin is a tetramer of two subunit types ((X2P2 m HbA). Despite having... 

Initially, it was suspected that the nitrophorins were insect hemoglobins. Indeed, they showed 45-48% homology with monomeric hemoglobins from insects, annelids, mollusks, nematodes, and even human 3 chains and leghemoglobin (44). However, in due time it became clear that these proteins were not globins at all, but rather, beta-barrel proteins called lipocalins (see Section III). As for the four nitrophorins, the sequences of NPl and NP4 are 90% identical, whereas those of NP2 and NP3 are 79% identical NPl and NP2, however, are only 38% identical. 

Figure 1 shows the Raman spectrum of Hb obtained with 406.7-and 413.1-nm excitation and the spectrum of monomeric, four-coordinate Ni protoporphyrin in aqueous micellar solution (9). Excitation at 413.1 nm is at resonance with the red component of the split Soret band of Ni-reconstituted hemoglobin at 406.7 nm the blue component of the Soret band is selectively probed. Comparison of the spectra shows that two sets of marker line frequencies exist. One set (labeled 4 in Figure 1) is enhanced by resonance with the blue Soret component the other set (labeled 5) is enhanced by excitation of the red Soret component. Thus, the shifts in the core-size lines in going from set 4 - 5 are -39 cm (i/-q at 1657 cm ), -20 cm cm ), and -34 cm 1 19 cm ). 

Red fibers provide for their ATP requirements mainly (but not exclusively) from fatty acids, which are broken down via 3-oxidation, the tricarboxylic acid cycle, and the respiratory chain (right part of the illustration). The red color in these fibers is due to the monomeric heme protein myoglobin, which they use as an O2 reserve. Myoglobin has a much higher af nity for O2 than hemoglobin and therefore only releases its O2 when there is a severe drop in O2 partial pressure (cf p.282). 

The method of cryoreduction was applied to oxy-ferrous hemoproteins. In one study, the monomeric hemoglobin from Glycera dibranchiata was used. This hemoglobin is different from other hemoglobins not only due to its monomeric... 

Many proteins consist of a single polypeptide chain, and are defined as monomeric proteins. However, others may consist of two or more polypeptide chains that may be structurally identical or totally unrelated. The arrangement of these polypeptide subunits is called the quaternary structure of the protein. [Note If there are two subunits, the protein is called dimeric , if three subunits trimeric , and, if several subunits, multimeric. ] Subunits are held together by noncovalent interactions (for example, hydrogen bonds, ionic bonds, and hydrophobic interactions). Subunits may either function independently of each other, or may work cooperatively, as in hemoglobin, in which the binding of oxygen to... 

---