Hemoglobin quaternary

Figure 4.3 Myoglobin and hemoglobin quaternary structures. (Reprinted from Figure 4.2 of Cowan, J. A. Inorganic Biochemistry, An Introduction, 2nd ed., Wiley-VCH, New York, 1997. Copyright 1997, Wiley-VCH.)...

Figure 7.12 The change in hemoglobin quaternary structure during oxygenation. 

In some proteins, such as hemoglobin, separate polypeptide chains must associate for the chains to be functional. This forms a quaternary stmcture. 

The allosteric effect is seen in hemoglobin which can exist in two quaternary stmctural states oxygenated (R) or deoxygenated (T). The binding of one O2 or some other effector to one of the subunits stabilizes the R form as compared to the T form. Binding of a second and third O2 stabilizes it even further. 

CPR can be used to find continuous paths for complex transitions that might have hundreds of saddle points and need to be described by thousands of path points. Examples of such transitions include the quaternary transition between the R and T states of hemoglobin [57] and the reorganization of the retinoic acid receptor upon substrate entry [58]. Because CPR yields the exact saddle points as part of the path, it can also be used in conjunction with nonnal mode analysis to estimate the vibrational entropy of activation... 

Proteins may also Have a quaternary structure, in which neighboring polypeptide units stack together in a specific arrangement. The hemoglobin molecule, for example, has a quaternary structure of four polypeptide units, one of which is shown in Fig. 19.20. 

THE ALLOSTERIC PROPERTIES OF HEMOGLOBINS RESULT FROM THEIR QUATERNARY STRUCTURES... 

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). 

Figure 6-5. Developmental pattern of the quaternary structure of fetal and newborn hemoglobins. (Reproduced, with permission, from Ganong WF Review of Medical Physiology, 20th ed. McGraw-Flill, 2001.)...

Most proteins contain more than one polypeptide chain. The manner in which these chains associate determines quaternary structure. Binding involves the same types of noncovalent forces mentioned for tertiary structure van der Waals forces, hydrophobic and hydrophilic attractions, and hydrogen bonding. However, the interactions are now interchain rather than infrachain (tertiary structure determination). The quaternary structure of hemoglobin (four almost identical subunits) will be discussed in Chapter 4, that of superoxide dismutase (two identical subunits) will be discussed in Chapter 5, and that of nitrogenase (multiple dissimilar subunits) will be discussed in Chapter 6. 

Quaternary structure the four separate chains Of hemoglobin assembled S3 into an oligomeric protein... 

All proteins have at least three levels of structure primary, secondary, and tertiary. Proteins with more than one polypeptide chain— hemoglobin and nitrogenase are examples—also possess quaternary structure. The primary. 

Hemoglobin provides an example of a protein possessing quaternary structure... 

Quaternary structure the tour separate chains of hemoglobin assembled into an oligomeric proteir ... 

Using the 241-cm value for the Ni-histidine frequency in Mb, the T- R shift from the Hb- Mb comparison is 5 cm. This value is consistent with the increase observed in a comparison of the corresponding Fe proteins and with the T R shifts based on other Fe hemoglobins (3-8 cm ) (31). The similarity of the increases observed in the metal-histi3 e frequencies for the nickel and iron hemoglobins indicates that the effect of quaternary structure on the Ni-histidine bond is similar to the Fe case. Also, the effect of the protein conformation change is virturally independent of the particular metal in the porphyrin core. 

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