Alexander Vershinin’s research while affiliated with Lomonosov Moscow State University and other places

Carotenoids first emerged in archaebacteria as lipids reinforcing cell membranes. To serve this function their long molecules have extremely rigid backbone due to the linear chain of usually 10 to 11 conjugated C=C bonds in trans-configuration — the length corresponding the thickness of hydrophobic zone of membrane which they penetrate as “molecular rivets”. Carotenoids retain their membrane-reinforcing function in some fungi and animals. The general structure of carotenoid molecule, originally having evolved for mechanical functions in membranes, possess a number of other properties that were later used for independent functions. The most striking fact is that these properties proved to fit some new functions to perfection. — The polyene chain of 9—11 double bonds absorbs light precisely in the gap of chlorophyll absorption — function as accessory light-harvesting pigments in all plants; — Unique arrangement of electronic levels owing to the by polyene chain structure makes carotenoids the only natural compounds capable of excitation energy transfer both (i) from carotenoid excited state to chlorophyll in the light-harvesting complex and (ii) from triplet chlorophyll or singlet oxygen to carotenoid in photosynthetic reaction centers — protection of RC from photodamage. The linear system of conjugated C=C bonds provides high reducing potential of carotenoid molecules making them potent antioxidants in lipid formations. Still, there is a lack of evidence of the chemical antioxidant function of carotenoids, especially in higher organisms; most data demonstrate an antioxidant ability rather than a function. Carotenoids have many other independent biological functions, including: specific coloration patterns in plants and animals, screening from excessive light and spectral filtering, defense of egg proteins from proteases in some invertebrates; the direct carotenoid derivative — retinal — acts as visual pigment in all animals and as chromophore in bacteriorhodopsin photosynthesis, retinoic acid in animals and abscisic acid in plants serve as hormones. All these functions utilize various properties (mechanical, electronic, stereospecific) of a single structure evolved in bacteria for a single membrane-reinforcing function, thus demonstrating an example of pure evolutionary preadaptation. One of the practical conclusions that can be reached by reviewing uniquely diverse properties and functions of carotenoids is that, when considering possible mechanisms of their effects in organisms (e.g., anticarcinogenic action), all their functional traits should be taken into account.

Carotenoids in eight species of freshwater and sea mollusks were investigated. In the nonreproductive organs of all species, only all-trans C40-xanthophylls were found. Carotenes are limited to hepatopancreas. No carotenoid derivatives or carotenoids with < 10 conjugated double bonds were detected. Carotenoids in molluskan cells are present in all subcellular fractions; the major part of them is located in plasma membrane. There are no special carotenoid-containing pigmented granules (“cytosomes” “carotenoxysomes”) in molluskan cells. Comparison of both Raman and absorption spectra of carotenoids in situ with those in CHCI3 suggests that pigments are dissolved in lipid matrix of membranes and not bound to proteins. No changes of carotenoid content or carotenoid pattern in Dreissena polymorpha, Unio pictorum and Viviparus contectus were observed during 10 days of starvation. There were no changes in isolated gills within 2 days as well. In the freshwater species with the exception of D. polymorpha, carotenoid content changes after the fast water temperature changes: with elevation of temperature, the carotenoid content in organs increases and vice versa, without any change in carotenoid composition. This phenomenon is shown to be due to rearrangement of pigments between the hepatopancreas and other organs. The results suggest that the role of carotenoids in molluskan tissues is not connected with their chemical transformations. The most probable function of carotenoids in mollusks is the stabilisation of cell membranes' fluidity.

1.1. In embryos of all stages of development to early pluteus only one carotenoid, all-trans β-echinenon, was detected.2.2. The data of Raman and absorption spectroscopy indicate that echinenon in embryo is probably dissolved in lipid formations and not bound to protein.3.3. During development, the decrease of echinenon content to 50% of the initial level was observed. The antioxidant role of echinenon in embryo is proposed.