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Carotenoids
Published in Ruth G. Alscher, John L. Hess, Antioxidants in Higher Plants, 2017
Kenneth E. Pallett, Andrew J. Young
It is clear that, in vitro, carotenoids have the ability to scavenge singlet oxygen and other highly reactive and potentially lethal oxygen species. The main photo-protective role of these pigments in photosynthetic systems may be through the direct quenching of the triplet-state sensitizer (chlorophyll or bacteriochlorophyll).50 It was also concluded that, in vivo, if carotenoid function were restricted to the scavenging of singlet oxygen, then a significant proportion of bacteriochlorophyll molecules would be irreversibly photooxidized through triplet sensitization. Furthermore, only partial photoprotection would be achieved because (1) the efficiency of this process would depend on the proximity of molecular oxygen to carotenoid and (2) the carotenoid would be competing for the singlet-oxygen energy with other components of the photosynthetic apparatus.35 Direct quenching of the triplet-state chlorophyll molecule, thus preventing the generation of singlet-oxygen in the first place, provides a much more efficient and effective protective strategy. Certainly the ability of membrane-bound carotenoids to scavenge for exogenous sources of singlet oxygen and free radicals, such as those produced in the presence of atmospheric pollutants, must be severely limited.
Crystallization of Purple Bacterial Antenna Complexes
Published in Hartmut Michel, Crystallization of Membrane Proteins, 1991
Richard J. Cogdell, Kevin J. Woolley, Linda A. Ferguson, Deborah J. Dawkins
The light-reactions of bacterial photosynthesis take place in and on the highly pigmented intracytoplasmic membranes.3,4 The actual light-absorbing pigments (bacteriochlorophylls and carotenoids) are organized into two main types of pigment-protein complex.5,6 The majority form the light-harvesting system and funnel absorbed radiant energy to a specialized few, called reaction centers, where that energy is trapped and used to drive photosynthesis. The bacteriochlorophylls and carotenoids are noncovalently bound to intrinsic membrane proteins, and whether a given pigment molecule is destined to fulfill a reaction center or antenna function is solely determined by which apoprotein it is bound to.
Trial watch: an update of clinical advances in photodynamic therapy and its immunoadjuvant properties for cancer treatment
Published in OncoImmunology, 2023
Mafalda Penetra, Luís G. Arnaut, Lígia C. Gomes-da-Silva
Only a relatively small proportion of clinical studies involve novel photosensitizers that have emerged from recent research. Examples of such molecules include, deuteporfin, a porphyrin derivative, the ruthenium-based complex TLD1433 and the bacteriochlorins, padeliporfin and redaporfin. Bacteriochlorins, in particular, appear to represent a promising class of new chemical entities due to their strong near-infrared absorption that enables the treatment of deeper lesions. Padeliporfin (WST11, Tookad®) is a semi-synthetic molecule derived from bacteriochlorophyll α found in benthic bacteria. It exhibits high absorption at 763 nm (ε = 1.1 × 105 M−1 cm−1) and fast body clearance, with a half-life in the range of a few minutes, which significantly limits the risk of skin photosensitivity3. Its fast clearance enables its use only in vascular-PDT protocols with tumor illumination occurring immediately after its infusion. Among the novel molecules without approval by any regulatory agency, padeliporfin (Tookad®) is the photosensitizer that has experienced more research, accounting for 11% of the trials (Figure 2a). It is worth noting that Tookad® was authorized by EMA in 2017 for the treatment of early-stage prostate cancer, but the FDA did not approve it76–80. In December 2021, Steba biotech withdrew the application submitted to EMA to extend the use of Tookad® in prostate cancer from the treatment of low-risk to intermediate-risk patients81. Currently, clinical trials also include patients with upper tract urothelial carcinoma, as listed in Tables 2 and 3.