The Amino Acid Composition of the 

 Haemoglobins of the Blood and Muscle 



of the Horse 



G. R. TRISTRAM 



The respiratory proteins of blood {haemoglobin) and muscle (myo- 

 globin) have parallel functions, and it is attractive to conjecture that 

 myoglobin, molecular weight 17,000, might be a precursor of 

 haemoglobin, molecular weight 68,000. Early centrifugal studies 

 led T. Svedberg 1 to advance this suggestion ; - a similarity is also 

 suggested by x-ray analysis of single crystals. It is clear, however, 

 that only by the accurate estimation of the relative amino acid 

 compositions of the two proteins might the validity of such a 

 hypothesis be confirmed. Recent work in the Department of Bio- 

 chemistry, Cambridge, in which the amino acids were estimated by 

 a variety of modern methods, previously tested by the analysis of 

 ad hoc mixtures of amino acids, has suggested that the two proteins 

 are completely dissimilar in amino acid composition. The present 

 analyses of myoglobin show significant differences from those 

 previously reported, particularly with regard to the sulphur con- 

 taining amino acids in the protein. 



SOURCE OF PROTEINS AND METHODS OF ANALYSIS 



Haemoglobin — The amino acid data reported in Table /were collected 

 from the literature, care being taken to select values which had been 

 obtained by the analysis of well characterized samples of this protein. 



/ The values for the basic amino acids are taken from H. T. 

 Macpherson 2 and were obtained by electrodialysis, arginine and 

 histidine being estimated ultimately by colorimetry and lysine by means 

 of a specific decarboxylase (cf Gale 7 ). 



2 The dicarboxylic acids, leucine, glycine and tyrosine were ob- 

 tained by G. L. Foster 8 using isotope dilution. 



3 The hydroxyamino acids were obtained by M. W. Rees 3 using his 

 modification of the Nicolet-Shinn procedure. This worker also 

 estimated amide-N. 



4 Proline, alanine and phenylalanine were obtained by partition 

 chromatography of the acetylamino acids (Tristram, unpublished 

 experiments). 



5 Various estimations of the sulphur acids have been reported and 

 there are wide divergencies in the values obtained by different workers. 



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