Chlorophyll functional properties

More details of the plastein reaction and its application to remove pigments such as chlorophyll, or to remove off-flavor components such as the beany taste of soybeans, are shown in Figure 2. The protein of the food system is solubilized and denatured (in order to achieve proteolysis), a protease is added, and the hydrolytic reaction is allowed to proceed. On partial hydrolysis of the protein the pigments and flavor constituents are released from the protein they are removed, the hydrolyzate is concentrated, and resynthesis and/or rearrangement of the amino acid sequence of the polypeptides is catalyzed by the same or a different protease. Resynthesis also can be carried out in the presence of added amino acid esters in order to improve the nutritional/functional properties of the protein. 

The effects of the fadP mutation on photosynthesis have been examined in some detail. Our preliminary results indicate that the mutation has no apparent effect on the growth rate or the rate of photosynthesis (expressed on a chlorophyll basis) at any temperature in the range of 10 C to 30°C (McCourt et al., 1986). The mutation also has no effect on the fluorescence characteristics and has only a slight effect on membrane fluidity as measured by fluorescence polarization studies. Measurements of temperature-induced fluorescence yield enhancement also failed to reveal a difference between the mutant and the wild-type. Thus, we have been unable to detect major effects on the functional properties of chloroplast membranes associated with a major reduction in trlenolc acids. This conclusion contrasts somewhat with the interpretation of other studies in which.the amount of chloroplast membrane unsaturation was reduced by growth in chemical inhibitors (Laskay and Lehoczki, 1986 Leech et al., 1985) or by catalytic hydrogenation (Thomas et al., 1986). Therefore, we consider it possible that the effects of these experimental treatments may be due to non-specific effects. 

This chapter brings together information concerning structural features, spectral characteristics, distributions, and functions of major chlorophylls in photosynthetic organisms. Other topics discussed include biosynthesis and degradation in senescent plants and ripening fruits and potential biological properties of chlorophylls. 

The biological functions of chloroplast ferredoxins are to mediate electron transport in the photosynthetic reaction. These ferredoxins receive electrons from light-excited chlorophyll, and reduce NADP in the presence of ferredoxin-NADPH reductase (23). Another function of chloroplast ferredoxins is the formation oT" ATP in oxygen-evolving noncyclic photophosphorylation (24). With respect to the photoreduction of NADP, it is known that microbial ferredoxins from C. pasteurianum (16) are capable of replacing the spinach ferredoxin, indicating the functional similarities of ferredoxins from completely different sources. The functions of chloroplast ferredoxins in photosynthesis and the properties of these ferredoxin proteins have been reviewed in detail by Orme-Johnson (2), Buchanan and Arnon (3), Bishop (25), and Yocum et al. ( ). 

Dendritic derivatives of these macrocycles can be placed in the wider context of studies on metalloporphyrins with sterically hindered faces which have been designed in attempts to mimic the properties of heme proteins and chlorophylls, and there are suggestions that steric isolation of the metalloporphyrin nucleus is important in certain biological functions, The redox properties of metalloporphyrins are well-documented they are dominated by two, reversible one-electron transfers involving both the metal and the ligand. The first dendritic porphyrins of general structure 47 and their Zn complexes were reported by Inoue et al. who... 

Porphyrins are an interesting class of compounds used for the study of energy- and electron-transfer functions of the natural photosynthetic machinery. The interest in porphyrins is motivated in part by their photocatalytic activity and electronic properties.74 Porphyrins are also structurally related to chlorophyll. 

This effect of cholesterol on the location of guest molecules has been cited for chlorophyll a (36) and tetracaine (5) both molecules with specific biological function. In the present work we have been able to observe this effect over the physiological ranges of temperature and cholesterol concentration. Future experiments with other molecules would clarify if this property of cholesterol is generally applicable to other systems and, furthermore, if it extends to interactions between two molecules solubilized in a membrane. 

These two molecules were the antecedents of a variety of oligomeric porphyrin and chlorophyll derivatives which were constructed as mimics of the reaction center special pair. Many of these systems exhibit interesting optical properties which allow modelling of the electronic interactions within the special pair and/or the antenna function of chlorophyll, which involves singlet-singlet energy transfer... 

Other biomimetic reactions are based on the catalytic properties of metal ions. Many enzymes require metal ions that function, in one way or another, in oxidation-reduction processes. The wide range of such metal-ion reactions precludes mentioning more than a few in addition to the iron-porphyrin class, and in addition to chlorophyll, a number of enzymes require cobalamin as cofactor ferridoxin and high-potential iron proteins require iron-sulfur clusters, and nitrog-... 

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