104 MACROMOLECULAR COMPLEXES 



contribution of the digitonin micelle. Digitonin alone forms micelles 

 of minimum molecular weight equal to 75,000. Three such micelles 

 of digitonin are probably linked, yielding a molecular weight of 

 225,000 (Hubbard, 1954). If the digitonin micellar weight is sub- 

 tracted from the molecular weight of 265,000 for the complex, the 

 molecular weight of chloroplastin would be of the order of 40,000 

 (Table 3). Takashima (1952) crystallized from leaf extracts a 



TABLE 3 

 Analytical Ultracentrifuge Data 



* M is calculated from M' using the dry weight and per cent nitrogen. 



chlorophyll-lipoprotein complex with a molecular weight of 19,000, 

 determined from diffusion studies. The crystalline complex indi- 

 cated that there were two molecules of chlorophyll per lipoprotein 

 molecule. A chlorophyll "holochrome" isolated by Smith and Young 

 (1956) from bean seedlings {Phaseoloiis vulgaris) in glvcerine- 

 KOH at pH 9.6 suggests a molecular weight of the order of 400,000.^ 

 For the chloroplasts of the algal flagellates Euglena and Poterio- 

 chromonas, the average molecular weights calculated from the 

 geometry of the chloroplast and the pigment concentration were 

 21,000 and 37,000, respectively. Using the interference microscope, 

 molecular weights were calculated to be of the order of one-half of 

 these values for the in vivo chloroplast. The molecular weight for 

 chloroplastin, calculated from its sedimentation, nitrogen, pigment 

 concentration, and dry weight, is of the order of 40,000 (Wolken, 

 1956b). The chloroplastin data implv that there is one chlorophyll 

 molecule to one protein molecule, although the possibility of two or 

 more chlorophyll molecules cannot be excluded (Table 4). Frey- 

 Wyssling predicts that there are 16 molecules of chlorophyll to one 



"The molecular weight of this complex is now reported to be 1 X 10*^ (Smith, 

 1959). 



