Ecto-ATPase of Erythrocyte Plasma Membrane in Black Sea Fishes and Factors Affecting Its Activity

The effect of erythrocyte sizes and protein-lipid, phospholipid, and fatty acid compositions of plasma membranes on the activity of the membrane ecto-ATPase was studied in two cartilaginous (Raja clavata, Dasyatis pastinaca) and eight teleost species (Scorpaena porcus, Uranoscopus scaber, Symphodus tinca, Diplodus annularis, Neogobius melanostomus, Spicara flexuosum, Trachurus mediterraneus, Gaidropsarus mediterraneus) of Black Sea fishes. The relationships between the high ecto-ATPase activity and the erythrocyte sizes were shown for both cartilaginous and teleost fish species. A higher relative protein content was found in membranes of the Black Sea rays, which probably indicates an evolutionary trend of decreasing proportion of the protein component and increasing lipids in teleost fishes. It was determined that fish erythrocytes with high protein content in the membrane have higher ecto-enzymatic activity. Plasma membrane phospholipids of fish erythrocytes are represented by five families: phosphatidylcholine (PC), phosphatidylethanolamine (PEA), phosphatidylserine, monophosphoinositide, and sphingomyelin. The high content of phospholipids and, in particular, PC and PEA in plasma membranes of fish erythrocytes is the basis for the formation of their bilayer matrix. Plasma membranes with a higher content of saturated fatty acids exhibited a higher ecto-ATPase activity, which indicated an important role of the enzyme in the physiology of the cell membrane and the blood flow in general.