Publisher Summary This chapter explores that the changes that take place in the protein molecules during denaturation constitute one of the most interesting and complex classes of reactions that can be found either in nature or in the laboratory These reactions are important because of the information they can provide about the more intimate details of protein structure and function They are also significant because they challenge the chemist with a difficult area for the application of chemical principles The chapter reviews that the denaturation is a process in which the spatial arrangement of the polypeptide chains within the molecule is changed from that typical of the native protein to a more disordered arrangement The chapter also discusses the classification of protein structures: primary, secondary, and tertiary structures The primary structure is that expressed by the structural chemical formula and depends entirely on the chemical valence bonds that the classical organic chemist would write down for the protein molecule The secondary structure is the configuration of the polypeptide chain that results from the satisfaction of the hydrogen bonding potential between the peptide N-H and C=O groups The tertiary structure is the pattern according to which the secondary structures are packed together within the native protein molecule The term “denaturation” as used in this chapter is indented to include changes in both the secondary and tertiary structures

Some factors in the interpretation of protein denaturation.

Publisher Summary The chapter reviews the results obtained from measurements of hydrogen exchange (H–H, H–D, and H–T) in proteins and related compounds. The slowness of the rate of hydrogen exchange in a protein, relative to the exchange rate observed with simple peptides under the same experimental conditions is closely related to the conformation of the protein molecule in aqueous solution. Quantitative measurements of the rate of hydrogen exchange in a given protein, under specified experimental conditions, provide a multiparameter characterization of the protein conformation (or distribution of conformations) present under these conditions. Moreover, the chapter discusses the experimental techniques that have been used to measure quantitatively the rate of hydrogen exchange. The chapter also discusses arguments that support case, as the mechanism of exchange of the slowly exchanging hydrogen atoms.

Hydrogen exchange in proteins.

Publisher Summary This chapter reviews that the simplest way of accounting for the absorption spectrum of a protein is as the sum of the spectra of its components. This gives results which are often good approximations to the observed protein spectrum. The assumption of additivity is basic for useful analytical applications of spectral measurements. It discusses that in another perspective, the failure of perfect additivity of the component absorptivities affords the possibility of obtaining structural information about proteins. The absorptivity of the peptide bond can change by as much as a factor of two with a change in the conformation of a peptide chain. Since the absorptivity of aromatic side chains is much less sensitive to environmental change, correspondingly, more sensitive techniques are required to measure the small changes which do occur. The nature and limitations of the structural information resulting from both peptide-bond and side-chain absorption are discussed. Absorption spectra can occasionally be a useful tool in the identification of unusual structural features in proteins and polypeptides. Several such applications are also explained in this chapter.

Ultraviolet spectra Of Proteins and Amino Acids

Publisher Summary This chapter reviews that titration curves do not represent just another way of physically characterizing a protein molecule. More than most other physicochemical methods that are in common use, titration studies tend to emphasize individual differences among proteins, and this is reflected in the chapter. The chapter contains experimental procedures of general utility in the determination of titration data. The foundation for any study of hydrogen ion dissociation in proteins is the electrometric titration curve. To obtain such a curve, one begins with a protein solution of known concentration, at an arbitrary reference pH, adds to it varying amounts of a strong acid or a strong base, and then measures the new pH attained. In a separate experiment, or by means of calculations based on similar experiments, one determines how much acid or base is needed to take a solution, which does not contain protein, but otherwise has the same initial pH, ionic strength, and volume. The difference between the two amounts is the amount of acid or base that is bound to the protein in going from the reference pH to the final pH: a plot of this quantity versus the final pH is the desired titration curve. In plotting this curve, OH - ions bound are counted as H + ions dissociated a procedure, which is always permissible in aqueous solutions.

Myron L. Wagner

Papers

Hydrogen Ion Equilibria of Lysozyme1,2

The Consecutive Constants for the Association of Cadmium with Imidazole1, 2