The Biochemical Function of Cells 409 



ficantly different. This difference is not only to be found before flowering but 

 remains present during the period of ripening of the seeds and maturation of 

 the tubers. 



THE COMMON FEATURES OF THE QUANTITATIVE 



AMINO ACID COMPOSITION OF THE PROTEINS 



OF DIFFERENT STRUCTURES 



As well as these differences in chemical composition and catalytic activity we 

 may observe many common features in structures of different origins. This is 

 based on the amino acid composition of the proteins. The qualitative amino 

 acid composition of the proteins of the structures of the photosynthesizing organs 

 is just the same for all classes of plants. This applies to the proteins of the leaves 

 of monocotyledonous and dicotyledonous plants and to the proteins of algae of 

 all classes. We have not found any information as to the amino acid composition 

 of photosynthesizing bacteria. 



Among the amino acids of which the proteins of the photosynthesizing organs 

 are composed, 17-18 have been identified (some by chromatographic methods), 

 which are common to the proteins of various organisms. These are: aspartic 

 and glutamic acids, serine, threonine, glycine, alanine, valine, leucine, isoleucine, 

 phenylalanine, tyrosine, proline, tryptophan, methionine, cystine, arginine, 

 histidine and lysine [53-56]. 



In the overall composition of the proteins of the plastids which we isolated, 

 and in an individual protein-containing compound (a lipoprotein) obtained from 

 the leucoplasts and chloroplasts of the sugar-beet, the same 18 amino acids were 

 fovmd as in the proteins of leaves or algae [57-61]. 



It would be interesting to compare the amino acid compositions of different 

 plant chromoproteins. As yet, however, only the most stable complexes of protein 

 with pigment have been isolated, namely the phycobiiins — phycoerythrin from 

 red algae (Porphyra tenera and Callithamnion rybosum) and phycocyanin from 

 blue-green algae (in particular from some species of Oscillatorid) [62-65]. 



The nature of the bond between the chlorophyll and the protein has not been 

 established. The chlorophyll-protein complex is unstable and the problem of its 

 isolation has not yet been solved. Some authors have cast doubt on the nature 

 of the crystalline chlorophyll-protein compoimd which has recently been iso- 

 lated by Takashima [66-68] from various classes of plants. Thus Krasnovskii & 

 Brin [69] believe that these crystals are chlorophyll crystals and the protein 

 and other substances are contaminants mixed with them. 



The amino acid composition of phycocyanin has been determined chromato- 

 graphically by Wassink & Rageth [63]. As well as thirteen common amino acids 

 they found three vmknown compounds as indicated by position on the chromato- 

 gram. These findings were confirmed by Fujiwara [65] on the basis of the appear- 

 ance of extra peaks during the quantitative determination of amino acids by the 

 methods of Moore & Stein [85]. 



However, the question of whether there are uncommon amino acids, which 

 are not found in higher plants, in the proteins of blue-green algae, cannot be 

 answered conclusively without a full identification of the compounds which 



