88 IntraccUiilar Extractives [Sept. 



No precursor of creatin is known. It is possible that it Is 

 derived from arginin vvhich is chemically closely related to it, but 

 no evidence of such change has been found. 



Von Fürth and Schwartz'^ recently found that cardiac muscle 

 of the horse contains much less creatin than does its skeletal muscle, 

 but rather more purins and carnosin. They also noted that the 

 amount and character of the extractive nitrogen was the same in 

 normal and in fatigued dog muscles. Apparently then the extrac- 

 tives are not involved or affected in the ordinary contraction metab- 

 olism. They are, however, intimately connected with the life of 

 the muscle cells. 



VII. INTRACELLULAR ENZYMES 



Alfred P. Lothrop 



Enzymes are colloidal in nature and do not dialyse through 

 parchment paper or do so with extreme slowness. It has been 

 claimed by some that in Solution they are electrically charged. 

 Being colloids they tend to carry down with them, by adsorption, 

 constituents of the Solutions from wliich they are precipitated. It 

 is very difficult to obtain pure enzymes unassociated with'other 

 substances. Whether the enzymes are proteins or not is still uncer- 

 tain. Some of the purest preparations have been found not to give 

 the characteristic protein reactions but the reactions may have been 

 so faint as to be overlooked. In very recent work on invertase^ 

 it was found that as long as the enzyme remained active it gave 

 the biuret, Millon and xanthoproteic reactions, suggesting that the 

 essential part of the ferment is a protein. Very pure preparations 

 of pancreatic amylase were found by Sherman and Schlesinger to 

 give pronounced xanthoproteic, tryptophan, biuret and Millon tests. 

 Water Solutions coagulated on boiling but the filtrates gave a rose 

 pink reaction in the biuret test.^ Some of the enzymes are 

 secreted in an inactive form or zymogen and are activated by a 

 co-enzyme or kinase. Their action is markedly influenced by 

 temperature and other conditions, the reaction of the liquid being 

 especially important biologically. The products of their own 



* Matthews and Glenn: Journal of Biological Chemistry, 191 1, ix, p. 29. 



* Sherman and Schlesinger: Journal of the American Chemical Society, 191 1, 

 xxxiii, p. 1195. 



