^ COMPOSITION OF CHLOROPLASTS 1743 



He found 13.8% N in proteins from chloroplast matter, against 14.5% in 

 those from the cytoplasm. The chloroplast matter contained 4.6% ash, 

 0.5% P, and 1.13% S; the cytoplasmic matter, 3.1% ash, no P, and 

 1.03% S. The amino acids were nearly the same in proteins from both 

 sources, the cytoplasm containing slightly more lysine and glutamic acid, 

 and slightly less histidine (c/. table 14.1 V). 



Sisakyan, Bezinger and Kuvaeva (1950) used paper chromatography 

 to identify sixteen amino acids in chloroplast proteins. Osipova and 

 Timofeeva (1950^) found that chloroplast proteins reduce more ferricyanide 

 than cytoplasmic proteins, and that their capacity to absorb chlorophyll 

 from alcoholic solution parallels their reducing capacity. After oxidation 

 with ferricyanide, chloroplast proteins lost about three-fourths of this 

 capacity and their reducing power became the same as that of proteins 

 from the cytoplasm. When chloroplast proteins absorb chlorophyll, 

 their capacity to be oxidized by ferricyanide is largely lost, indicating that 

 chlorophyll blocks their reducing groups. 



Osipova and Timofeeva (1950'-^) observed changes in chloroplast 

 composition caused by nitrogen deficiency. With nitrogen supply re- 

 duced to one-quarter of the normal, protein concentration went down from 

 70 to 26%, while the amount of starch rose from 3 to 30%. 



Godnev, Shlyk and Tretjak (1952) determined, using P (32) as tracer, 

 the phosphorus content in chloroplasts in relation to the total phosphorus 

 content in the leaf, and found 6, 15 and 22% in oats, rye and lettuce, re- 

 spectively. Of the total phosphorus found in chloroplasts, about 3% were 

 contained in phospholipids; the mass ratio chlorophyll : phospholipide 

 was 5.5 in rye and 2.5 in lettuce — much higher than required by Hubert's 

 model (fig. 46) ; this discrepancy was noted before (Vol. I, p. 375) in the 

 analysis of Chibnall's data. 



Menke (cf. p. 384) suggested the possible presence in chloroplast mate- 

 rial of nudeoproteids. Euler, Bracco and co-workers (1948, 1949) first 

 found ribonucleic acid in the products of precipitation of isolated chloro- 

 plast material by lanthanum salts. Metzner (1952i'') confirmed the pres- 

 ence of nucleic acids in chloroplasts from Agapanthus umbellatus by cy to- 

 chemical tests. He noted that the staining of grana with basic dyes can be 

 prevented by extraction with agents which dissolve nucleic acid, and that 

 the digestion of chloroplast proteins by trypsin can be prevented by pre- 

 cipitation of nucleic acid with lanthanum salts, or with streptomycin. 

 Metzner surmised that the stroma — which contains phosphatides, as indi- 

 cated by its capacity to form myelin figures (cf. section 2) — contains ribo- 

 nucleic acid (often associated with phosphatides) ; while staining evidence 

 indicates that the grana may contain both the ribonucleic and the desoxy- 

 ribonucleic acid. McClendon (1953) noted that in the fractionation of 



