Power of Crystalline Ovalbumin arid Serum Albumin. 



25 



than 02 per cent. The error in the estimation of the dried coagulum from 

 variations observed might amount to 2-5 nigrm. in 0'5 grm., or a maximum 

 -error of 0'5 per cent. A fluctuation of 0'25 of a degree in the specific rotation 

 •value would be the maximum experimental error permissible. It will be 

 found that the results agree more closely than this as a rule. The variations 

 in specific rotation produced by variations of Ph, as shown in Table VII, 

 for example, amount to several degrees. There seem to be two possible 

 explanations for this phenomenon. As Fischer has shown, the salts of 

 • amino acids have different optical rotations from the free acids themselves. 

 Now the isoelectric point must be taken as the natural point of neutrality 

 of the protein molecule ; that is, the point at which the dissociation con- 

 stants of the protein as an acid and as a base balance. By the addition 

 of acid or alkali, salts would be formed on amino acid groupings, and the 

 measure of salt formation would be the governing factor in change of 

 optical rotation. This is certainly not so on the alkaline side, for beyond 

 the first drop in rotation, further addition of alkali has no obvious effect. 

 Likewise the addition of acid can change the rotation once, and once only, 



■ apparently. 



The second explanation, as suggested by Eobertson, that a tautomeric 

 ■equilibrium exists in certain amide groupings is most forcibly emphasised by 

 the slow change in optical rotation in alkaline solution, and, further, by the 

 reversibility of the phenomenon generally from either side of the isoelectric 

 point. That such a tautomerism is probable from other reasons has been 

 very fully shown by Eobertson, in supporting his theory of protein ionisation. 

 Furthermore, such an equilibrium would be governed by the hydrogen ion 

 'Concentration, and not by the quantity of acid molecules present. The 

 slight changes in the acidity of the medium might thus account for the 

 -fluctuations of the specific rotations observed and recorded in the literature. 



Crystalline Serum Albumin. 



Crystalline serum albumin was first prepared by Giirber in 1894 by the 

 •direct application of Hofmeister's method to horse serum. Merely from the 

 appearance of the crystals, Giirber concluded that three albumins occur in 

 serum, all crystallisable. Michel, in 1896, introduced a slight modification in 

 the technique, and determined the coagulation temperature and specific 

 ■rotation of the crystalline product. Hopkins and Pinkus (1898) mention 



■ the fact that it is possible to obtain crystals from serum by the acid method, 

 ■but the time required is one to several days. Krieger (1899) shortly after- 

 wards suggested the use of H2SO4 in place of acetic acid without any 

 « quantitative data. In his paper on pure ovalbumin, Hopkins mentions that, 



