chlorophyll-a and alloxanthin

Photosynthetic organisms had to evolve diverse mechanisms of light-harvesting to supply photosynthetic apparatus with enough energy. Cryptophytes represent one of the groups of photosynthetic organisms combining external and internal antenna systems. They contain one type of immobile phycobiliprotein located at the lumenal side of the thylakoid membrane, together with membrane-bound chlorophyll a/c antenna (CAC). Here we employ femtosecond transient absorption spectroscopy to study energy transfer pathways in the CAC proteins of cryptophyte Rhodomonas salina. The major CAC carotenoid, alloxanthin, is a cryptophyte-specific carotenoid, and it is the only naturally-occurring carotenoid with two triple bonds in its structure. In order to explore the energy transfer pathways within the CAC complex, three excitation wavelengths (505, 590, and 640 nm) were chosen to excite pigments in the CAC antenna. The excitation of Chl c at either 590 or 640 nm proves efficient energy transfer between Chl c and Chl a. The excitation of alloxanthin at 505 nm shows an active pathway from the S

Topics: Chlorophyll; Cryptophyta; Energy Transfer; Phycobiliproteins; Xanthophylls

Potential sex and/or gametogenic stage differences in the metabolism of chlorophyll-a and carotenoids in the brown mussel Perna perna of southern Brazil were studied using high performance liquid chromatography (HPLC). Carotenoids derived directly from diet (phytoplankton) were fucoxanthin plus diatoxanthin (diatoms), alloxanthin (cryptophytes) and zeaxanthin (mainly cyanobacteria). Females accumulated carotenoid-diols and epoxides (~3-4 mg/g-dry wt.) while males had much lower concentrations (~0.7 mg/g-dry wt.). An antioxidant/free radical scavenging role is proposed for carotenoids in females. Mean ratios of chlorophyll plus derivatives (Chlns-a) to carotenoids for male and female P. perna were 50:1 and 4:1, respectively. The higher ratio in males relates to both higher carotenoid contents in females plus higher total Chlns-a in males (~22 mg/g-dry wt.), relative to the females (~4 mg/g-dry wt.). Chlorophyll-a metabolism in both sexes followed two distinct pathways. First, cyclization of pyropheophorbide-a gave 13(2), 17(3)-cyclopheophorbide-a-enol (CPPaE) which was further oxidized to hydroxy-chlorophyllone. Second, chlorophyll-a derivatives retaining the 13(2)-carbomethoxy moiety were oxidized to purpurin-18 which was hydrolyzed to chlorin-p(6). In both cases, metabolism of dietary chlorophyll-a was oxidative and derivatives could either serve as antioxidants or merely be the results of non-specific digestive processes.

Topics: Animals; Carotenoids; Chlorophyll; Chlorophyll A; Chromatography, High Pressure Liquid; Epoxy Compounds; Female; Male; Molecular Structure; Perna; Phytoplankton; Porphyrins; Xanthophylls; Zeaxanthins