Chemical Composition of Human Myoglobin 



fractions. The most evident difference concerns the basic nitrogen, 

 minor differences also being found in the non-amino nitrogen of the 

 filtrate (imino-acids + 1/2 tryptophan nitrogen) and in the nitrogen 

 of the monoamino and dicarboxylic acids. 



Table II gives the data for percentages of iron, sulphur, histidine, 

 lysine, arginine, cysteine and tryptophan. These data show that human 

 haemoglobin and myoglobin have the same iron content and probably 

 the same prosthetic group (protoferrohaem). The proteins differ in 

 amino-acid content, myoglobin being poorer in arginine and richer 

 in lysine and tryptophan : only small differences in sulphur and cysteine 

 content were noted. In consequence the molecular ratios are different 

 (see second part of Table II). Human myoglobin has one residue of 

 cysteine only, in good agreement with a minimum molecular weight 

 of 17,000 (c/the constancy of cysteine content of myoglobin of different 

 species, claimed by Roche 6 ). 



The differences in chemical composition are accompanied by differ- 

 ences in the physico-chemical behaviour of the two pigments. For 

 example, the positions of the spectral absorption bands and the resist- 

 ances to alkaline denaturation are different 16 ' 17 > 18 . On the latter 

 property was based a spectrophotometric method for the simultaneous 

 determination of the two pigments 19 . 



Table III 



Arginine I Sulphur and Histidine /Iron Ratios of Haemo- 

 globins and Myoglobins of different Species 



* The data for ox and dog myoglobin and haemoglobin are calculated from figures 

 given by Roche 8 . 



119 



