PROTEINS. JO/ 



The nude o proteins occur principally in animal and vegetable 

 cells, and following the destruction of these cells they are found 

 in the fluids of the body. These proteins are discharged into the 

 tissue fluids by the activity or disintegration of cells. Combined 

 with the simple protein in the nucleoprotein molecule we find 

 nucleic acid, a body which contains phosphorus and which yields 

 purine bases and pyrimidine bases (thy mine ^ cytosine and uracil) 

 upon decomposition. The so-called nucleins are formed in the gas- 

 tric digestion of nucleoproteins. 



Wheeler-Johnson Reaction for Uracil and Cytosine. To 

 about 5 c.c. of the solution under examination add bromine water 

 until the color is permanent. 1 In case the solution contains only 

 small quantities of cytosine or uracil, it is advisable to remove the 

 excess of bromine by passing a stream of air through the solution. 

 Now add an excess of an aqueous solution of barium hydroxide 

 and note the appearance of a purple color. 



Very dilute solutions do not give the test. Under these condi- 

 tions the solution should be evaporated to dryness, the residue dis- 

 solved in a little bromine water and the excess of bromine removed. 

 Then upon adding an excess of barium hydroxide a decided bluish- 

 pink or lavender color will appear in the presence of as small an 

 amount as o.ooi gram of uracil. 



In testing solutions for cytosine, it is preferable to warm or boil 

 the solution with bromine water, and after cooling the solution to 

 apply the test as suggested above, being careful to have a slight 

 excess of bromine present before adding barium hydroxide. 



The phospho < proteins are called nucleo albumins in many classi- 

 fications and are grouped among the simple proteins. They are 

 considered to be "compounds of the protein molecule with some, 

 as yet undefined, phosphorus-containing substances other than a 

 nucleic acid or lecithin." The percentage of phosphorus in phos- 

 phoproteins is very similar to that in nucleoproteins but they differ 

 from this latter class of proteins in that they do not yield any 

 purine bases upon hydrolytic cleavage. Two of the common phos- 

 phoproteins are the caseinogen of milk and the ovovitellin of the 

 egg-yolk. 



The hcemoglobins (chromoproteins) are compounds of the pro- 

 tein molecule with haematin or some similar substance. The prin- 



1 Avoid the addition of a large excess of bromine inasmuch as this will 

 interfere with the test. 



