Pheophytin, formation

Siefermann-Harms D (1990b) Photooxidation and pheophytin formation of chlorophyll in the Hght-harvesting Chl-o/b-protein complex exposed to fatty adds Protective role of the intact apoprotein. In Baltscheffsky M (ed) Current Research in Photosynthesis, Vol 11, pp 245-248. Kluwer Academic Publishers, Dordrecht... 

Water activity has been shown to have a definite influence on the rate of degradation of chlorophyll in freeze-dried, blanched spinach puree [73]. At 37°C and an higher than 0.32, the most important mechanism of chlorophyll degradation was conversion to pheophytin. At lower than 0.32, the rate of pheophytin formation in spinach was low. The rate of chlorophyll-a transformation was 2.5 times faster than chlorophyll-. The study of the degradation of chlorophyll as a function of a . pH, and temperature in a spinach system... 

PHOTOOXIDATION AND PHEOPHYTIN FORMATION OF CHLOROPHYLL IN THE LIGHTHARVESTING CHL-a/b-PROTEIN COMPLEX EXPOSED TO FATTY ACIDS ... 

As shown in Fig. 1, photooxidation of LHC-bound Chl-a at pH 7.8 and pheophytin formation of LHC-bound Chl-a at pH 1.3 are hardly enhanced by fatty acids of 6 to 12 carbon atoms, whereas fatty acids of 14 to 18 carbons accelerate these reactions significantly. Within the Cj g fatty acids tested, desaturation improves the ability of the acids to destroy photo- and acid stability of the LHC. These results do not appear to be explained simply by differences in the partitioning of the different fatty acids between lipophilic LHC and aqueous solvent. Namely, while the molar solubility of saturated fatty acids in both, lipophilic cyclohexane and water decreases by a factor of 20 for acids from 12 to 18 carbons, the solubility ratio for either fatty acid in these solvents changes only slightly (calculated from Ref. 4). 

The fatty acids tested here cause little change of the fluorescence excitation spectrxim of LHC for Chl-a emission at 680 nm and of the emission spectra of the LHC for Chl-b excitation at 470 nm or predominant carotenoid excitation at 455 nm. This is in contrast to the effect of Triton X-100 at 250 pM, i.e. a concentration enhancing photooxidation and pheophytin formation of Chl-a at a degree similar to 30 mM linoleic acid (Fig. 1). The results show that the efficient energy transfer from carotenoids and Chl-b to Chl-a taking place between the highly ordered pigments of intact LHC (2) is maintained in the presence of fatty acids. 

Middle Pheophytin formation was monitored as absorbance decrease at 675 nm after lowering the pH to pH 1.3 with concentrated HCl. The rate of pheophytin formation after 3 min at pH 1.3 is presented. 

Photooxidation and Pheophytin Formation of Chlorophyll in the Light-Harvesting CHL-a/b-Protein Complex Exposed to Fatty Acids Protective Role of the Intact Apoproteins 245... 

Zaprometov, M. N., N. V. Zagoskina and T. F. Koretskaya. Effect of some precursors on the formation of phenolic compounds in tea plant tissue cultures. Fiziol Rast 1976 23 1274. Higashi-Okai, K., S. Otani and Y. Okai. Potent suppressive activity of pheophytin A and B from the non-polyphenolic fraction of green tea (Camellia sinensis) against tumor promotion in mouse skin. Cancer Lett 1998 129(2) 223-228. 

A rise in absorbance at 1250 nm is interpreted as formation of the bacteriochlorophyll cation radical BChl+ in the special pair. Other spectral changes support the formation of BPh as the first reduction product (A- in Eq. 23-31). However, this is thought to occur in two steps323 with the monomeric BChl (BA in Fig. 23-31B) receiving the electron in 2.8 ps and passing it to the pheophytin (Phe ( >A in Fig. 23-31B) in 0.7 ps (Eq. 23-32 corresponding steps for PSII of green plants are also shown). 

Add 100 to 200 mg MgO or MgC03 to the sample (step 1) to neutralize plant acids and prevent pheophytin a formation. 

It is important to note that chlorophylls are converted to pheophytins in the presence of acids (unit F4.t). Formation of a significant... 

Successful formation ofCu2+ or Zn2+ pheophytin would result in only one major chromatographic peak (>90% of total peak area). The presence of other peaks most likely results from incomplete complexation or allomerization (oxidation) of the chlorophyll molecules. In these instances further chromatographic purification (based on A Iternate Protocol) may be necessary in order to achieve the desired degree of analytical purity. 

The importance of bioexcimers (bioexciplexes) in the photochemistry of biological compounds has been also emphasized. Computation of potential energy curves modeling the complex pheophytin-quinone shows the relevance that stabilization caused by the formation of rr-stacked excited dimers, that is, excimers (exciplexes) and the corresponding presence of conical intersections, have to provide... 

Steric hindrance, attributed to the phytol chain of pheophytin, may decrease the rate of complex formation. In the study by Berezin and Koifman (20), pheophorbide a reacted 4 times faster with copper(II) ion than did pheophytin a in ethanol at 25°C. Moreover, electrostatic interaction of the C-7 propionic... 

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