The Chemical Composition of Human 

 Myoglobin 



A. ROSSI-FANELLI 



These researches have demonstrated the possibility of obtaining 

 human myoglobin from skeletal muscles by a relatively simple pro- 

 cedure ; they have also shown that human myoglobin crystals differ 

 in form from those of haemoglobin, and some crystallographic data 

 for human myoglobin are given. Human myoglobin and haemo- 

 globin differ in the chemical nature of their globins. The nitrogen 

 distribution {by the Van Slyke method) is different in the two 

 pigments. The amino-acid content is also different, myoglobin being 

 poorer in arginine and richer in lysine and tryptophan. 



The haemoglobin of muscle (myoglobin) is similar to that of blood, 

 but differs from it in certain properties, such as position of the spectral 

 absorption bands, affinity for oxygen and carbon monoxide, and the 

 Bohr effect. Moreover both pigments have highly specific physiological 

 functions. Haemoglobin and myoglobin both contain the same 

 prosthetic group (protoferrohaem), and it was consequently presumed 

 that the difference between the two pigments lay in the difference 

 between their globins. In 1940 we gave the first experimental evidence 

 for this hypothesis 1 ' 5 , showing that the protein components of haemo- 

 globin and myoglobin (obtained in crystalline form from horse myo- 

 cardium) are chemically different substances. The most striking 

 differences were observed in the arginine, lysine, and tyrosine content, 

 but the differences in proline, hydroxyproline, and tryptophan were 

 also noteworthy. J. Roche 6 contributed a good deal to this work. 

 Studies on the chemical nature of myoglobin, however, included only 

 those derived from the more common laboratory animals (horse, ox, 

 dog, pig) ; human myoglobin was neglected because attempts to 

 prepare it in crystalline form had been unsuccessful. Nevertheless 

 during recent years human myoglobin has been crystallized by D. L. 

 Drabkin 7 , by H. Theorell 8 , and by the present author 9 , using a 

 variety of different procedures for the isolation of the protein. Our 

 method, already used successfully for the crystallization of horse and 

 bovine myoglobins, is based on the different solubilities of haemoglobin 

 and myoglobin in ammonium sulphate solutions, a fact already ob- 

 served by V. E. Morgan 10 , E. Cohn 11 , J. Roche 6 , and others. This 

 method does not involve any previous perfusion of the muscle and 

 may be applied to any type of skeletal muscle. 



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