The Biochemical Function of Cells 411 



the physiological state, as has been shown in a large number of recent investi- 

 gations [50-52, 60, 61, 86]. 



Table 5 shows the amino acid composition of the proteins of different classes 

 of plant organism — blue-green and red algae, and diatoms as well as green algae 

 and others, the leaves of both monocotyledonous and dicotyledonous higher 

 plants. For comparison we have also given figures for cytoplasmic proteins, the 

 total protein of the chloroplasts and also the individual chromoprotein complexes, 

 phycoerythrin and phycocyanin. As may be seen from the figures given, the 

 amino acid content of the proteins varies, sometimes quite considerably. The 

 proteins of photosynthesizing organs also show some common features such as a 

 relatively high content of basic amino acids (Table 5 and [62, 86]). 



This all suggests that the qualitative biochemical variabiHty of protoplasmic 

 structures derived from different sources is, most probably, associated with the 

 more intimate structural pecuharities of the proteins which determine their 

 specificity. The discovery of these extremely fine differences in the proteins 

 will only be possible after the estabhshment of the amino acid sequence and 

 other structural features of the protein molecules. 



STRUCTURE AND BIOCHEMICAL FUNCTIONS 



In understanding the biochemical functions of cells, great importance is 

 attached to the study of the structural organization and the manifestation of 

 enzymic activity [71-75]. 



Experimental evidence shows that the functional and, in particular, the enzymic 

 activity depend, not only on structural organization, but also on the conditions 

 of the mediimi imder the influence of which the formation of the structures 

 takes place. This concept may be illustrated by facts derived from the study 

 of the activity of enzymes of the cyclophorase system in the structural elements 

 of plant cells. 



Recent investigations have estabhshed, beyond doubt, the existence, in the 

 structural formations of plant cells, of a cyclophorase system of enzymes, which 

 brings about the transformation of di- and tri-carboxyHc acids [76-80]. Cyclo- 

 phorase activity was foimd in structures isolated from both etiolated and green 

 plants. However, the question of its locaHzation in any particular structures 

 cannot be considered to be conclusively settled. Some workers take the view 

 that cyclophorase activity is concentrated solely in structures of a mitochondrial 

 type. Others beheve that cyclophorase activity is concentrated in the chloroplasts. 

 Naturally the identification of the structural carriers of particular biochemical 

 functions is a task of the utmost importance for the elucidation of their part in 

 cellular metabolism. 



We have estabhshed [81] that cyclophorase activity in green plants grown 

 under indoor illimiination (Fig. 3, curves I) is concentrated mainly in the 

 fraction of particles which come down within the range of 3000-8500 g. The 

 absorption of O2 in this fraction of particles at the expense of the oxidation of 

 succinic acid amounted to 145 /d. Og/mg N after i hour, and was associated with 

 the absorption of inorganic phosphorus. The shght activity (22 /d. Og/mg N) 



