PREPARATION, PRESERVATION AND ACTIVATION OF CHLOROPLASTS 1561 



contain no enzyme; while the over-all ratio chlorophyll : enzyme (and thus, 

 in theory, also the limiting rate in strong light) remain unchanged. 



These results are suggestive, but will not be quantitatively convincing 

 until more is known about the nature and composition of chloroplast frag- 

 ments of different size. Are they pieces of protein lamellae with chloro- 

 phyll attached to them? Are they irregular chunks of grana, containing 

 pieces of both proteidic and lipoidic phases? Do they contain any of the 

 proteins (or lipoproteids) of the stroma? Even the average chlorophyll 

 content of the chloroplast material is uncertain unless it has been de- 

 termined in an aliquot of the same sample as that used for photochemical 

 studies. The uncertainty becomes as great as a factor of ten when we deal 

 with chloroplast fragments selected by fractional centrifugation, or another 



" o 50 TOO Volume in &> xlO^ 150 



Fig. 35.15A. Oxygen evolution by suspension of chloroplast fragments as function of 

 their average size, in the presence of quinone (after Thomas, Blaauw and Duysens 

 1953). 



fractionation method. Particularly uncertain — and challenging — is the 

 situation in the case of the chloroplast-free, phycocyanine-bearing blue- 

 green algae, and of the chloroplast-containing, phycoerythrin-bearing red 

 algae. What happens in the fragmentation of the chromoproteids? It 

 seems that they are almost completely separated from the chlorophyll- 

 bearing, insoluble fragments {cf. chapter 37A, section 3); the resulting 

 suspension shows no Hill reaction (^^an Norman et al., 1948). McClendon 

 and Blinks (1952) showed that the loss of phycobilins can be prevented by 

 crushing the cells in a medium containing high-molecular compounds, such 

 as Carbowaxes (c/. p. 1549); the material then shows well-sustained Hill 

 activity (McClendon, 1954). 



The results obtained by electron microscopy and ultracentrifugation of 

 dispersed chloroplast material from the higher plants, blue-green algae, and 

 purple bacteria will be presented in chapter 37A. We will see there that 

 the morphological picture is as yet far from clear, particularly in respect 

 to the submicroscopic localization of the various pigments. The correla- 

 tion between the structure and the photochemical activity of the various 

 dispersions is a matter for future exploration. 



