SECTIONAL TRANSACTIONS.— B. 349 



tions are illustrated by an account of the synthesis of glutathione and of 

 recent work on the introduction of additional amino-acid residues into 

 protein molecules. 



Attention is called to the important possibilities of constitutional work 

 on proteins which have been opened up by the method of stepwise degrada- 

 tion recently introduced by Bergmann. 



Brief reference is made to alternative theories of protein structure which 

 have been advanced from time to time. It is concluded that the peptide 

 theory alone has adequate experimental support, but it is pointed out that 

 the peptide linkage is insufficient by itself to account for all the properties 

 of proteins ; the possibility of the occurrence of subsidiary linkages must 

 be admitted and it appears certain that an orderly arrangement must exist 

 within the protein molecule, satisfying definite spatial requirements. 



It is suggested that further progress in the study of proteins will be most 

 effectively made by the application of physical and biochemical methods, 

 but that this application must be based on the foundation which has been 

 laid and is being extended by organic chemistry. 



Dr. K. Linderstr0m-Lang. — Proteolytic enzymes. 



Dr. W. T. AsTBURY. — X-ray interpretation of protein structure. 



Of the two broad sub-divisions of protein structure, the fibrous and the 

 non-fibrous, X-ray investigation has of recent years offered a view that 

 allows us to look at the stereochemical picture, not as two apparently unre- 

 lated halves, but as a single intelligible whole. All proteins are fibrous in 

 the molecular sense, the structural unit being the polypeptide chain, and in 

 those proteins which exist naturally as fibres the chains generally lie in groups 

 parallel, or simply related, to the visible fibre-axis. They may be stereo- 

 chemically fully extended, as in silk fibroin, or constricted into regular 

 linear folds, as in the unstretched or a-forms of the hair protein keratin and 

 the muscle protein myosin, and the basis of the remarkable long-range 

 elasticity observed in such cases is simply the pulling-out or further folding 

 of the normal molecular configuration. The ultra-centrifuge, X-rays, etc., 

 agree in finding the molecules of the soluble, and often visibly crystalline, 

 proteins to be by no means obviously fibrous, but rather massive ' globular ' 

 bodies. The solution of this paradox comes from the interpretation of the 

 phenomenon of protein denaturation, which is found by X-rays always to 

 result in the production of polypeptide chain-bundles which can then some- 

 times be drawn parallel, or ' spun,' to form macroscopic fibres structurally 

 analogous, especially on stretching, to the native protein fibres. Denatura- 

 tion is thus in general the breakdown of a specific folded configuration 

 of polypeptide chains, and the structure of the ' globular ' proteins is 

 apparently a logical generalisation in two or three dimensions of the regular 

 linear folds first demonstrated in the molecules of the fibrous proteins. 

 The contraction of hair or muscle represents no other than an intermediate 

 stage between the fully-extended configuration of silk fibroin and the 

 multiple folds of the globular proteins. 



The regularly periodic structure of the proteins revealed by X-rays, 

 especially in such cases as feather keratin and the recently identified tobacco- 

 mosaic virus, is now finding its counterpart in the realisation, through the 

 analytical work of Bergmann and others, that there are certain clear-cut 

 stoichiometric relations between the proportions of the constituent amino- 

 acid residues. 



