86 



MACROMOLECULAR COMPLEXES 



those in which the photosynthetic pigments are located in small 

 granules, chromatophores, will be here referred to as chloroplasts. 

 It is technically difficult to isolate chloroplasts from other cellular 

 components, and precise data on their chemical composition are not 

 easily obtainable. A summary of the data on isolated chloroplasts 

 ^rom a variety of plants is given in Rabinowitch (1945, 1951, 1956). 

 In all of these studies of composition, particularly of the pigments 

 and their concentration, the state of the plant cells, age, nutrition, 

 temperature, and light conditions are extremely important. 



Fig. 1. Diagram of microspectrophotometer. L, light source; G, mono- 

 chromotor; M, microscope with reflecting optics; C, photoconductive cell; 

 A, amplifier; D, oscilloscope. 



A range of values on a dry-weight basis from 35 to 55 per cent for 

 the protein, 18 to 37 per cent for the lipids, and 5 to 8 per cent for 

 the inorganic materials is given for a variety of plant chloroplasts. 

 Studies are being made to determine the kinds of proteins and their 

 amino acid composition (Sissakian, 1958). Two cytochromes, cyto- 

 chrome f and cytochrome b^, together, can make up as much as 20 

 per cent of the chloroplast's total protein content. Nucleic acids 

 (both RNA and DNA) are also reported to be in the chloroplasts; 

 experimental values range from 0.3 to 3.5 per cent on a dr\'-weight 

 basis. 



The chlorophyll pigments constitute about 5 to 8 per cent of the 

 chloroplast (although concentrations as high as 20 per cent have 

 been reported), and the carotenoids are about 2 per cent. Chloro- 

 phyll a occurs in all plant chloroplasts, but other isomers are also 



