Amino Acid Composition of Haemoglobins of Blood and Muscle of Horse 



(68,000) and certain similarities in crystal structure (cf Kendrew (p. 148)) 

 made it attractive to suggest that the simpler protein might be a pre- 

 cursor of the more complex molecule. Whilst their overall amino acid 

 compositions are dissimilar, the possibility that myoglobin may be the 

 precursor of a portion of the haemoglobin cannot be excluded. That 

 this is not so seems certain by virtue of the findings of Porter and 

 Sanger (p. 121) that whereas haemoglobin contains six intramolecular 

 chains each v/ith a valine residue as the terminal amino group, myo- 

 globin has but a single chain with a glycine residue in the corresponding 

 position. 



The proteins haemoglobin and myoglobin must therefore be regarded 

 as strictly independent molecules, with parallel functions in blood and 

 muscle respectively, and as far as amino-acid composition is con- 

 cerned similar only in their content of haem and in the overall basic 

 character of the protein moieties. 



My thanks are due to Dr H. T. Macpherson, Mr M. W. Rees and 

 Mr G. Wiltshire for permission to make use of unpublished analyses and 

 to Professor A. C. Chibnall for advice and valuable criticism. 



Received September 1948 



REFERENCES 



1 Svedberg, T. The Ultracentrifuge (1936) Clarendon Press, Oxford 



2 Macpherson, H. T. Bio-chem. J. 40 (1946) 470 



3 Rees, M. W. Bio-chem. J. 40 (1946) 632 



4 Tristram, G. R. Bio-chem. J. 40 (1946) 721 



5 Roche, J., Derrien, Y. and Vieil, H. Bull. Soc. chim. Biol. Paris 24 (1942) 1016 



6 Rossi-Fanelli, A. Arch. Sci. biol. Napoli 26 (1940) 244 



7 Gale, E. F. Bio-chem. J. 39 (1945) 46 



8 Foster, G. L. J.biol.Chem. 159(1945)431 



9 Kuhn, R., Birkofer, L. and Quackenbush, F. W. Ber. dtsch. chem. Ges. 72 



(1939) 409 



10 Greenstein, J. J. biol. Chem. 128 (1939) 233 



11 Lyman, C. M., Moseley, O., Butler, B., Wood, S. and Hale, F. /. biol. Chem. 



166 (1946) 161 



12 Mirsky, A. E. and Anson, M. L. /. gen. Physiol. 19 (1936) 439 



13 Consden, R., Gordon, A. H. and Martin, A. J. P. Bio-chem. J. 42 (1948) 443 



14 Blumenthal, D. and Clarke, H. T. /. biol. Chem. 110 (1935) 345 



15 Bailey, K. Bio-chem. J. 43 (1948) 271 



16 Tristram, G. R. Advances in Protein Chemistry V (1949) Academic Press, 



New York 



113 



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