PHOTOSYNTHETIC PIGMENTS 35 



HAEMATIN COMPOUNDS PRESENT IN GREEN LEAVES 



In addition to the pigments concerned in the absorption 

 of light, another group of porphyrin compounds present in 

 the leaf is the haematins. Although present in molar con- 

 centrations less than one-hundredth that of chlorophyll, in 

 the leaf the haem pigments are in a greater concentration 

 relative to the respiratory activity than in other organisms. 



In addition to catalase, peroxidase, and the cytochromes 

 which occur throughout the plant (see Table 3.4), the leaves 

 of higher plants also contain two cytochrome components 

 believed to be characteristic of plant tissue. Acetone treat- 

 ment removes the chlorophylls and carotenoid pigments but 

 does not result in appreciable loss of the haematin com- 

 pounds. Direct spectroscopic examination of the acetone- 

 treated leaf preparation showed the presence of a non- 

 autoxidizable cytochrome. Fractionation of the pressed 

 juice from macerated leaves using ammonium sulphate 

 yielded both a non-autoxidizable and an autoxidizable cyto- 

 chrome component. The autoxidizable component had in 

 the reduced form an a band at 559-7 m/bi and was called cyto- 

 chrome 63 on account of some resemblances to cytochrome 

 Z>2 (a band 556-3 m^). The second component cytochrome/ 

 could not be extracted in an unmodified form from acetone 

 preparations from leaves, but was obtained from fresh leaves 

 ground with ethanol containing ammonia. Cold acetone was 

 added to the alcoholic solution when part of the/ component 

 could be obtained from the precipitate in aqueous solution 

 (Davenport and Hill, 195 1). Cytochrome/is non-autoxidiz- 

 able and gives no reaction with carbon monoxide. Its poten- 

 tial is more oxidizing than that of cytochrome c by about o-i 

 volt. The absorption spectrum of ferrocytochrome/is simi- 

 lar to that of cytochrome c, but the bands are more sharply 

 defined and lie 5 m/^ nearer the red end of thie spectrum. The 

 a band is asymmetric and in solutions more alkaline than 

 pH 9-0 it can be observed to split into two components, a 

 strong narrow band at 556 m^ and a narrow and weaker 

 band at 551 uifi; the effect is reversible up to pH 12, above 

 which denaturation of the protein occurs. The prosthetic 



