PHLOROTANNIN-PROTEIN INTERACTIONS

Tannins are one of the most broadly distributed types of plant seconda ry compounds, and have been the focal point for many studies of plant/ herbivore interactions. Tannins interact strongly with proteins. so th at the fate and effects of ingested tannins are in part dependent on t he mode of interaction of the tannin with dietary and endogenous prote ins in an herbivore's gut. We investigated the factors affecting the p recipitation of proteins by phlorotannins from three species of marine brown algae: Carpophyllum maschalocarpum, Ecklonia radiata, and Lobop hora variegata. Phlorotannins were precipitated by proteins in a pH-de pendent and concentration-dependent fashion. Precipitation also varied as a function of the presence of reducing agent, the type of phlorota nnin or protein used, and the presence of organic solvents such as hyd rogen bond inhibitors. Of particular significance was the ability of s ome phlorotannins to oxidize and form covalent bonds with some protein s. In contrast, under similar experimental conditions three types of t errestrial tannins (procyanidins, profisetinidins, and gallotannins) a pparently did not form covalent complexes with proteins. Our results s uggest several ways in which the biological activity of phlorotannins may vary as a function of the properties of the gut environment of mar ine herbivores. Moreover, we identify specific structural characterist ics of phlorotannins which affect their tendency to oxidize, and thus, their potential effects on marine herbivores.