Protein ionic bonds

Since this must inevitably involve interactions between the exterior surfaces of proteins, ionic bonding can be more important to quaternary structure than it is to tertiary structure. Nevertheless, hydrophobic (van der Waals) interactions have a role to play. It is not possible for a protein to fold up such that all hydrophobic groups are placed to the centre. Some such groups may be stranded on the surface. If they form a small hydrophobic area on the protein surface, there would be a distinct advantage for two protein molecules to form a dimer such that the two hydrophobic areas face each other rather than be exposed to an aqueous environment. 

Intramolecular ionic bonds between oppositely charged groups on amino acid residues in a protein... 

The overall distribution of lanthanides in bone may be influenced by the reactions between trivalent cations and bone surfaces. Bone surfaces accumulate many poorly utilized or excreted cations present in the circulation. The mechanisms of accumulation in bone may include reactions with bone mineral such as adsorption, ion exchange, and ionic bond formation (Neuman and Neuman, 1958) as well as the formation of complexes with proteins or other organic bone constituents (Taylor, 1972). The uptake of lanthanides and actinides by bone mineral appears to be independent of the ionic radius. Taylor et al. (1971) have shown that the in vitro uptakes on powdered bone ash of 241Am(III) (ionic radius 0.98 A) and of 239Pu(IV) (ionic radius 0.90 A) were 0.97 0.016 and 0.98 0.007, respectively. In vitro experiments by Foreman (1962) suggested that Pu(IV) accumulated on powdered bone or bone ash by adsorption, a relatively nonspecific reaction. On the other hand, reactions with organic bone constituents appear to depend on ionic radius. The complexes of the smaller Pu(IV) ion and any of the organic bone constituents tested thus far were more stable (as determined by gel filtration) than the complexes with Am(III) or Cm(III) (Taylor, 1972). 

Nucleic acids, proteins, some carbohydrates, and hormones are informational molecules. They carry directions for the control of biological processes. With the exception of hormones, these are macromolecules. In all these interactions, secondary forces such as hydrogen bonding and van der Waals forces, ionic bonds, and hydrophobic or hydrophilic characteristics play critical roles. Molecular recognition is the term used to describe the ability of molecules to recognize and interact bond—specifically with other molecules. This molecular recognition is based on a combination of the interactions just cited and on structure. 

Organisms deal with this situation by speeding up reactions with catalysts called enzymes. A catalyst affects the rate of a reaction but does not otherwise participate, so it is not chemically altered. Enzymes are usually proteins that temporarily bind the reactants in such a way as to bring them together in the correct position. This binding is not done with strong bonds such as covalent or ionic bonds, but with weaker attractions that are more easily broken. An enzyme usually catalyzes only one specific reaction since its shape and composition are generally such that it binds only a specific set of reactants. 

Bonds and Forces - These properties are the mediators affecting the changes in size and conformation. Van der Waal forces, ionic bonds, hydrogen bonds, covalent bonds, and hydrophobic bonds all play a part in the original protein structure as well as in the modifications leading to altered functionality. Adequate correlations of these with functional properties are the subjects of "Functional Evaluations" 3). 

Ionic bonding between charged amino acid side chains or as salt bridges, and 3) hydrophobic and related attractions along protein strands. 

Sefa-Dedeh and Stanley ( ) attributed decreases in solubility characteristics of cowpea proteins at low ionic strength to the formation of ionic bonds 1) within the protein molecule and... 

Figure 3.17 Types of bondings to plasma proteins that foreign compounds can undergo (A) ionic bonding, (B) hydro- B> phobic bonding, (C) hydrogen bonding,...

Non-covalent bonding includes hydrogen bonding, ionic bonds, or hydrophobic bonds. These types of bonding are involved in binding of chemicals to plasma proteins. They could also underlie the interaction between a chemical and a receptor or enzyme. Thus, the interaction between TCDD and the Ah receptor (AhR) and the intercalation of doxorubicin in DNA involve non-covalent bonds. 

Protein structure is stabilized by multiple weak interactions. Hydrophobic interactions are the major contributors to stabilizing the globular form of most soluble proteins hydrogen bonds and ionic interactions are optimized in the specific structures that are thermodynamically most stable. 

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... 

There are five classes of histones, which are positively charged small proteins that form ionic bonds with negatively charged DNA. Two each of histones H2A, H2B, H3, and H4 form a structural core around which DNA is wrapped creating a nucleosome. The DNA connecting the nucleosomes is called linker DNA, and is bound to histone H1. 

---