In vivo release of lectins from the green alga Ulva fasciata

The green alga Ulva fasciata Delile (Ulvaceae), after thawing from storage at -20 degrees C, has been used to study the in vivo biosynthesis and release of lectins. The alga was made to resume viable growth by immersion in a PBS buffer, pH 7.4, containing 0.01% w/v sodium azide and irradiating with a halophosphate lamp. The growing alga readily took up 14C leucine, when this was added to the buffer, as seen by a decrease in a sample count rate of approximately 8000 cpm over a period of twenty minutes. The transfer of the radioactivity fed algae into fresh PBS buffer resulted in 14C labeled proteins being subsequently released into solution. As well as observing changes in levels of radioactivity, the release of proteins was also monitored by UV absorption at 280 nm. Both techniques indicated an initial steady release over the first twelve hours, followed by a slower approach to a plateau value. Transfer of the algae that had undergone an initial period of protein release into a subsequent second and third volume of fresh PBS buffer produced similar UV absorption profiles, but the total quantities of material released were reduced. Identification of the released proteins was obtained from their ability to agglutinate red blood cells, which was inhibited by L-fucose, and their electrophoretic mobilities when compared with earlier isolated samples of the U. fasciata lectin. The reference lectin was obtained by affinity chromatography, following the selective precipitation of the water soluble algal proteins with ammonium sulfate. We postulate that the observed release profiles support the previously suggested concept that lectins have the ability to function as protection agents for living marine algae.