15 



On the Optical Rotatory Power of Crystalline Ovalbumin and 



Serum Albumin. ' 

 By Elrid Gordon Young, Ramsay Memorial Fellow. 



(Communicated by Prof. F. G. Hopkins, F.R.S. — Received July 6, 1921.) 



(From the Biochemical Laboratory, Cambridge University.) 



The need for a physical method by means of which it would be possible to 

 recognise a chemical individual of the protein group of compounds has 

 undoubtedly been one of the factors contributing to the difficulty of research 

 into the chemistry of the proteins. The present methods of chemical analysis 

 do not nearly approach sufficient accuracy to distinguish between successive 

 recrystallisations of a protein substance. The first serious effort to prove that 

 an individual protein could be isolated is to be found in the publication of 

 Hopkins (1900). It was here shown that a protein could be prepared with a 

 constant specific rotation for successive recrystallisations and for material 

 obtained from different sources. Unfortunately, this desirable physical 

 constant, which is independent of the degree of colloidal dispersion, has 

 been shown to vary with variations in physical and chemical conditions. 

 Thus Alexander (1896) found the specific rotation of certain globulins 

 varied according to the concentration of the protein and of salt present. An 

 investigation of this phenomenon by Pauli, Samec and Strausz (1914) con- 

 firmed the observations of Hopkins (1900) and of Osborne (1899) that the 

 presence of neutral salts has no influence on the optical rotation of a protein. 

 The addition of acids and of alkalies they found to increase the rotation of 

 polarised light, while the degree of change depended upon the nature of the 

 anion in the case of an acid and of the kation in the case of a base. These 

 observations were made, unfortunately, with the mixture of proteins contained 

 in ox or horse serum which had simply been dialysed until salt-free. The 

 nature of these changes may find explanation in a tautomeric equilibrium of 

 the lactam -lactim type in the protein main chain when in aqueous solution, 

 as suggested by Robertson (1912) and Sorensen (1912), and to which view 

 Pauli inclines. 



R — CO — NH — R — R— C(OH) = N — R. 



Lactam formula. Lactim formula. 



The determination of the specific rotation of crystalline ovalbumin as a 

 means of discovering its purity, as Hopkins had shown possible, was called 

 into question by Willcock (1908), on the basis of the test used to show when 

 the analysis sample had been washed free from sulphate. Using a ring test with 



