374 



CHLOROPLASTS AND CHROMOPLASTS 



CHAP. 14 



Additional data on the composition of leaf proteins can be found in 

 the investigations of Lugg (1938, 1939, 1940), Tristram (1939) and 

 Smith and Wang (1941). According to Hanson, Barrien, and Wood 

 (1941), the chloroplast proteins are rich in sulfur (about 70% of total 

 leaf protein sulfur being concentrated in the chloroplasts). 



Menke (1938) suggested that the thread-forming capacity of the 

 chloroplasts, described by Kiister (1935), points to the presence of long- 

 chain molecules. He found that 80% of the chloroplast proteins are 

 insoluble in water, hydrochloric acid and aqueous alkali; to extract them 

 one must use 60% alcohol with 0.3% sodium hydroxide. This protein 

 fraction is free of phosphorus. The small protein fraction which is 

 soluble in water contains some phosphorus (nucleophosphatides?). 



Observations on the floccu- 

 lation and electrophoresis of 

 suspended chloroplastic material 

 (Neish; Fishman and Moyer) in- 

 dicate isoelectric points between 

 3.7 and 4.7 (cf. page 386). 



The so-called "lipoid" fraction 

 (the ether extract and the ether- 

 alcohol extract) of chloroplastic 

 matter contains the pigments 

 (5-10% chlorophyll and 2-4% 

 carotenoids; cf. Chapter 15, page 

 411, for detailed data). The rest 

 of this fraction may include fatty 

 acids, aldehydes, fats, hydrocar- 

 bons, phytosterols, and phospho- 

 lipides. The latter are of special 

 interest because of the important 

 role which Hubert (1936) ascribed 

 to them in the structure of the 

 chloroplasts {cf. Fig. 46). 



Phospholipides are glycerides 

 which differ from fats in that the 

 glycerol is combined with only two 

 fatty acid radicals, the third hy- 

 droxyl being esterified by phos- 

 phoric acid (cf. Formula 14.1). 

 The first investigations into the 

 composition of the leaf lipoids 

 have been carried out by Channon 

 and Chibnall (1927), Chibnall and 



