Pheophytins absorption characteristics

Removal of the Mg from C. generates pheophytin hydrolysis of the phytol or farnesol ester (catalysed by chlorophyllase, EC 3.1.1.4) produces a water-soluble chlorophyllide. Removal of Mg from the chloro-phyllide produces a pheophorbide. All these compounds are intensely colored and fluoresce strongly in strictly anhydrous solution in an organic solvent. The characteristic absorption spectra are used to identify and quantify C. and their derivatives. In vivo, the absorption spectra are strongly affected by binding to proteins. Some C.-protein complexes of the thylakoid membrane have been isolated and identified. 

The spectral properties of the Ti-anion radicals of Chi and BChl and their respective magnesium-free analogs pheophytin (Pheo) and bacteriopheophytin (BPheo) are of considerable interest, since spectroscopic methods have detected the formation of the latter three radicals during the primary events of photosynthesis [49]. We have characterized the spectra of the anion radicals of Et-Pheo-a, Et-Chl-a, Et-BPheo-a and Et-BChl-a and have compared the calculated [33, 36, 37] and experimental spectra in Fig. 13. As shown in the figure, once again the absorption spectra display characteristic visible and Soret absorption regions, but the visible bands are generally much more structured than are those of either the neutral or cationic moieties. 

The absorption spectra of Phe a and 13 -hydroxy-Phe a are essentially identical (Fig. 1). In comparison to BPhe a, there are two characteristic blue-shifted Q -bands for the two plant-type pheophytins, and the Q -bands are blue-shifted by 70-80 nm, too. Unlike Phe a, [3-acetyl]-Phe a shows a split Soret-band as do the bacteriopheophytins. Providing the same assignments, they are red-shifted by 24 nm (B )and 28 nm (B ). The main peak of the Soret-band of Phe a is red-shifted by 52 nm compared to B of BPhe a. 

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