Amino Acid Composition of Haemoglobins of Blood and Muscle of Horse 



(differential oxidation — Rees in unpublished experiments). The values 

 reported in Table I may therefore require modification, but even if the 

 highest value for cystine-cysteine (1-0 per cent) be taken and it is 

 assumed that only cystine is present, then a maximum of 3 disulphide 

 groups may exist in the haemoglobin molecule. It is known however 

 that haemoglobin does contain SH groups (cf Greenstein 10 , Mirsky 

 and Anson 12 ) so that S-S cannot exceed two groups. Since the work 

 of R. R. Porter and F. Sanger (p. 121) suggests the presence of six 

 constituent chains in the haemoglobin molecule, it would appear that 

 either the distribution of the sulphur-containing amino acids requires 

 re-investigation, or that the intramolecular chains are cross-linked by 

 some system as yet unknown but which is covalent. 



Table II 



Distribution of Groups in Haemoglobin and Myoglobin 



Myoglobin Haemoglobin 

 Total No. of residues 146 580 



Mean residue weight 112 112-5 



Percentage distribution of groups 



Myoglobin — This protein was analysed in the above laboratory by 

 H. T. Macpherson 2 , M. W. Rees 3 , the author 4 and G. Wiltshire. 

 The last named estimated the dicarboxylic acids by a modification of 

 the ion-exchange method of R. Consden, A. H. Gordon and A. J. P. 

 Martin 13 . The myoglobin analyzed was identical with that used by 

 J. C. Kendrew (p. 148) for crystallographic studies. It was prepared 

 by Rees from horse heart muscle, being finally crystallized from 

 phosphate buffers. 



Ill 



