CHAPTER 24 – Evolution of Protein Molecules

IN 1966, I became interested in the amino acid sequences of cytochrome c molecules ([Jukes 1966][1]). I noted that these sequences differed in the cytochromes c of various species to an extent that seemed unnecessary from the standpoint of their function. I stated, “The changes produced in

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The neutral theory of molecular evolution.

Publisher Summary This chapter describes the present state of the studies of the molten globule state and its role in protein folding and physiological processes Recent data on the intermediates (equilibrium and kinetic), focusing attention on the molten globule state are discussed in the chapter The molten globule has a native-like overall architecture (folding pattern) without including the rigid packing of side chains It is separated by first-order phase transitions from both the native and the unfolded states and represents a third thermodynamic state of protein molecules It is a universal kinetic intermediate in protein folding; the structure of this intermediate is similar to the structure of the equilibrium molten globule It is predicted and confirmed experimentally that the molten globule state can exist in a living cell and plays an important role in a number of physiological processes

Molten globule and protein folding.

Determination of Tyrosine and Tryptophan in Proteins

Publisher Summary The chapter illustrates that the studies of hydrolytic agents have led to major advances in our knowledge of proteins, including the identification of the amino acid constituents of proteins and the development of the polypeptide concept of protein structure. These studies are now, for the most part, of historical interest, and provide an insight into protein hydrolysis. This is largely the result of three significant developments: (1) the discovery of chromatographic and electrophoretic methods for the examinatioin of the hydrolytic products of pure proteins; (2) the use of acids and enzymes as reagents for the systematic degradation of proteins into small peptides that are amenable to sequence analysis; and (3) the preparation of highly purified proteolytic enzymes that can be used for selective hydrolysis. The chapter mainly deals with the recent developments in the use of acids and enzymes for the hydrolysis of proteins, with particular emphasis on the hydrolytic methods, which are employed in amino acid sequence studies. Particular attention is given to those factors that must be considered in selection of a suitable hydrolytic reagent.

Hydrolysis of Proteins

Publisher Summary This chapter focuses on the accuracy of the peptide theory and on the possible existence of non- peptide bonds in proteins. Partition chromatography in the form of paper chromatography is a method that is identified as breakdown products of proteins where more peptides are used. This technique had been identified by the classical methods of organic chemistry. Three types of polypeptide chains are possible, open, cyclic and branched. There are two types of terminal residues, those with a free amino group and those with a free carboxyl group. The Dinitrophenyl (DNP) method is used for the separation and identification of peptides containing lysine. Elution can be effected with acid ethanol and the peptides subsequently fractionated on suitable partition chromatograms. The theoretical possibility exists that synthetic reactions may occur during the partial hydrolysis of proteins. Acid hydrolysis is the most used method of degrading proteins, and it is almost universally employed when amino acids are to be isolated or estimated, since it leads to complete hydrolysis with a minimum of destruction. Paper chromatography is preferred for the final fractionation of a simplified peptide mixture because of the good resolutions obtained, the ease and rapidity of technique, and the possibility of using the two-dimensional method. The chief disadvantage is that only a very small amount of each peptide can be obtained from a chromatogram, though it is usually possible to obtain sufficient material to determine the structure of di- and tri-peptides.

F. Sanger

Papers

The Arrangement of Amino Acids in Proteins