Читать книгу Molecular Mechanisms of Photosynthesis - Robert E. Blankenship - Страница 70

The metal‐free chlorophylls are known as pheophytins. The structures of pheophytin a and bacteriopheophytin a are shown in Fig. 4.5. In these compounds, two hydrogen ions replace the central Mg²⁺. Acidic conditions promote the displacement of the metal. Pheophytins are formed during the degradation of chlorophylls, so are often viewed as primarily breakdown products resulting from loss of the central metal. However, small amounts of pheophytin are an essential component of some reaction center complexes and are almost certainly made in a specific pathway, although it is not known. Pheophytin is somewhat easier to reduce than the corresponding chlorophyll, so it can function as an electron acceptor at a place in the sequence of electron carriers where chlorophyll will not work.

Figure 4.5 Chemical structures of pheophytin a and bacteriopheophytin a.