CHLOROPHYLL-PROTEIN RATIO 389 



Wassink, Katz, and Dorrestein (1939) made extensive spectroscopic 

 investigations of colored colloidal extracts obtained by grinding purple 

 bacteria {Thiorhodoceae and Athiorhodoceae) (cf. Chapter 21, Vol. II). 

 The spectrum of a suspension in egg albumen, in particular, was found 

 to be practically identical with that of intact bacteria. 



Whereas the spectra of alcoholic solutions of bacteriochlorophyll 

 were identical for all strains, the spectra of intact cells and of colloidal 

 protein-pigment solutions varied considerably from strain to strain. In 

 solution, bacteriochlorophyll has only one absorption peak in the infrared, 

 but the cell suspensions and colloidal extracts showed two such peaks, 

 with humps indicating additional bands. This can be interpreted as 

 evidence of complex formation by one and the same pigment with several 

 different proteins. 



3. The Chlorophyll-Protein Ratio 



On the strength of the experiments described in the preceding section, 

 many authors have assumed the existence of a chlorophjdl-protein 

 compound in the chloroplast as definitely established, and have suggested 

 different names for it. Mestre (1930) proposed the name phyllochlorin, 

 which is, however pre-empted for a compound of the chlorin class. As 

 mentioned on page 385, Stoll (1936) introduced the name chloroplastin, 

 while French (1940) preferred photosynthin, because chloroplastin suggests 

 a limitation to chloroplast-bearing plants, with the exclusion of algae 

 and bacteria. Perhaps chloroglobin (or chromoglohin) would be a better 

 name because of its analogy with hemoglobin. 



However, before any such name is adopted, a proof of constant and 

 reproducible size and composition of the chlorophyll-protein complex 

 appears desirable. As we have mentioned in the preceding section, 

 the size of the protein-lipoid-pigment particles prepared by the disinte- 

 gration of the chloroplasts in water varies widely from experiment to 

 experiment. We shall now consider the composition of these particles, 

 particularly their chlorophyll-protein ratio. Smith (1941) suggested 

 that three molecules of chlorophyll a and one molecule of chlorophyll h 

 are associated with one Svedberg unit of protein (molecular weight 

 ~ 17,000) in leaf extracts (prior to their "clarification" by detergents). 

 This conclusion was based on analyses showing 16.3 g. chloroph3'll per 

 100 g. protein in the chloroplastic matter from Spinacia and 15.5-16.5 

 g. per 100 g. protein in that from Aspidistra, and on the fact (c/. Chapter 

 15) that the average ratio [a] : [b] in the higher plants is close to 3. 

 However, very different chlorophyll-protein ratios have been found by 

 other observers, and the [a] : [b] ratio also can vary widely (the h 

 component being altogether absent in most algae; c/. page 405). 



