32 



Mr. E. G. Young. On the Optical Rotatory 



The third and fourth values are practically identical when the limits of 

 accuracy of the determination of the albumin are considered. It is, 

 moreover, of great interest to note that the value coincides with that, 

 obtained by the alcohol-ether method, as recorded in Table X. 



Discussion of Results. 



There has been much discussion for years past as to the possible chemical 

 alliance of proteins with fats or lipoids in the blood. This is particularly 

 true of eu-globulin, and Hardy and Gardiner have briefly indicated that it is 

 possible that serum albumin is chemically bound to cholesterol esters and 

 pigments in serum. Now, it is necessary to recognise that, in determining 

 the value for specific rotation, we really have only allied rotatory power 

 with coagulable material. That is to say, that identical weights of 

 coagulated material in undenatured form from the two preparations, if 

 made into solutions of identical concentration, would have an identical 

 rotation. If cholesterol were present in chemical union with one albumin,, 

 then it must of necessity have an inappreciable effect upon the total 

 observed rotation, and be completely volatilised during the drying operation.. 

 By reason of the fact that cholesterol is optically Isevo-rotatory, these- 

 circumstances are, to say the least, improbable. One other possibility must, 

 be mentioned. The cholesterol, or other fatty material with which the 

 albumin was chemically associated in serum, might be split off in the act of 

 crystallisation. The " milieu " for such a chemically conceived separation is, 

 indeed, nothing more vigorous than a concentrated (NH^SC^ solution and 

 very dilute acetic acid at a temperature of 20°. At the same time,, 

 proteins are extremely labile molecular structures. There is, furthermore,, 

 one piece of concrete evidence. On first crystallisation direct from serum r 

 there is an insoluble residue of a fatty nature. The deposition of this 

 residue is completely inhibited by previous ether extraction. The crystals 

 themselves are most probably a pure protein, and of the same nature as- 

 found for ovalbumin, although differing in their chemical structure of amino 

 acids, as indicated by the difference in specific rotation. 



The solutions used for the determinations of specific rotation recorded 

 were never entirely free from pigment. The solutions from the first method! 

 were much clearer than those from the second. In the latter, the successive 

 recrystallisations diminished the pigmentation of the solution but little. 

 I have tried many methods of removing pigment by adsorbents without 

 success, e.g., kieselguhr, charcoal and freshly precipitated barium sulphate. 

 If the crystals are produced very slowly, the first crop formed is always 

 much more coloured than subsequent ones. The amount of pigment. 



