The aim of the project is to understand the function of globin X (GbX) in the activation of the sodium/proton exchange across the erythrocyte membrane of fish. This exchange is oxygen dependent and activated by adrenergic stimulation; however the exact mechanism is unknown. It has been suggested that membrane binding of haemoglobin would be involved but such haemoglobin has not been found yet.Recently we found that GbX mRNA is expressed in red blood cells of fish. GbX is a membrane-bound vertebrate globin that is unique within the vertebrate (haemo-) globin superfamily and its cellular functions are not well understood because practically all available data on GbX are based on mRNA abundance.In a multidisciplinary approach we will combine the molecular and functional findings on GbX and oxygen-dependent membrane transport in a completely new fashion with an environmental focus. The study includes in vitro approaches in red blood cell culture and in vivo experiments in different fish species to unravel the cellular functions of GbX. The central research question is if GbX regulates the oxygen affinity of haemoglobin by affecting the ion transport in nucleated erythrocytes of fish.The research proposed in this proposal has the potential to make a valuable contribution to the field of red blood cell research by applying state-of-the-art techniques which have not been applied to nucleated erythrocytes before. The underlying aims are to explain the molecular basis of oxygen transport and to unravel adaptation mechanisms of fish species to environmental challenges. The project thereby touches several of the biggest issues today since global warming, oxygen limitation and pollution highly impact aquatic ecosystems worldwide. In particular marginal Seas such as the Baltic Sea, the second largest brackish water area in the world, are affected. The host of the project will be Prof Mikko Nikinmaa at the University of Turku, Finland.