1548 



PHOTOCHEMISTRY OF CHLOROPHYLL 



CHAP. 35 



Storage, to 50 or 20% of the initial value. The results show that the loss of 

 activity must be due to the deterioration of enzymatic components and 

 not to changes in the chlorophyll-protein complex. 



Some success has been achieved with chemical stabilization. Milner, 

 French et al. (1950) noted a preserving effect of sucrose and of ethylene 

 glycol, Holt, Smith and French (1950) studied the effect of various concen- 

 trations of propTjlene glycol at 0° C. and pH 6.5. The best results were ob- 

 tained with a 10% solution ; the activity loss in this medium was about 



100 



> 



t- 

 o 

 < 



_i 

 < 



2 



75 



50 



25 



V 



Chloroplasts 

 ■o- 



Dispersion 

 o— 



-i_ 



3 4 



DAYS 



Fig. 35.10. Inactivation of chloroplast fragments and of their colloidal dis- 

 persions (after Milner, French, Koenig and Lawrence 1950). 



one half of that without propylene glycol. Diethylene glycol, n-propyl 

 alcohol, isopropyl alcohol, glycerol (10%) and ethanol (10-50%,) had only 

 a weak effect, or no effect at all. Strychnine, which stimulates the dye re- 

 duction by chloroplasts (Table 35.XI), had no preserving effect. 



According to Arnon et al. (1954), whole chloroplasts prepared in ethyl- 

 ene glycol show no C*02 fixation in Hght (in contrast to those prepared in 

 0.5 M glucose or 0.35 M NaCl) . 



A much stronger stabilizing effect than that of propylene glycol is 

 produced by methanol (fig. 35.9). This was noted by Milner, French et al. 

 (1950) when studying fractional coagulation of colloidal chloroplast dis- 

 persions. They observed that not only did these sols withstand consider- 

 able methanol concentrations without coagulating, but their photochemical 

 efficiency was stabilized. 



