THE INDIVIDUAL GROUPS OF PROTEINS 447 



THE COAGULABLE PROTEINS OF MUSCLE. 



The solid matter of muscle consists essentially of proteins, the 

 principal other constituents being fat, extractives (creatine and other 

 nitrogenous substances) and lactic acid Lean meat has the following 



average composition : 



Water 75 



{Protein 20 

 Extractives 3 

 Salts i 



Living muscle consists of a semi-fluid muscle plasma which is 

 faintly alkaline in reaction to litmus. As the result of death the 

 soluble proteins undergo clotting rigor mortis and become in- 

 soluble ; the reaction becomes acid due to the formation of lactic acid. 

 The coagulation is accelerated by acids and by a rise of temperature 

 and does not occur in weak alkaline solutions or in the absence of salts. 



During life, the coagulation change seems to be brought about by 

 lactic acid and the disappearance of the insoluble protein is owing to 

 its re-solution by the lactic acid which also disappears and is again 

 built up into the soluble protein. 



The disappearance of rigor mortis after death is probably due to 

 solution of the insoluble protein by a proteoclastic enzyme which 

 converts it into metaprotein and other derivatives. 



Two soluble proteins only one according to Mellanby * are pre- 

 sent in living muscle : (i) Paramyosinogen, (2) myosinogen in the 

 proportions of one-fifth and four-fifths respectively. These are con- 

 verted by clotting into myosin, the former directly, the latter through 

 the stage of soluble myosin, thus 



Paramyosinogen .- ^ 



(or myosin) I Myosin 



Myosinogen -> Soluble myosin _> f (or muscle fibrin) 



(or myogen) ' 



Paramyosinogen and Myosinogen. 



Preparation. 



Fresh muscle, veal, or the muscles of a rabbit freed from blood by perfusing 

 the vessels through the aorta with -9 per cent, sodium chloride solution, are 

 chopped up finely and treated with "9 per cent, sodium chloride solution. 



The extract is slightly acid due to the presence of lactic acid which can 

 be tested for by Uffelmann's test or Hopkins' test (p. 112). The extract is 

 treated with three -fourths of its volume of saturated ammonium sulphate. 

 The paramyosinogen is precipitated. It is dissolved and reprecipitated 

 several times, or separated out by dialysis. The protein can then be pre- 

 pared as described under ovoglobulin and serum globulins. 



The filtrate from the paramyosinogen is saturated with ammonium sulphate. 

 The precipitate of myosinogen so formed is purified by solution and repre- 

 cipitation. 



1 J. Physiol., 1908, Proc. 



