UV-induced changes of structural and functional properties of blood lactate dehydrogenase isoenzymes in free state and in the presence of serotonin

Photoinduced changes of structural and functional properties of lactatedehydrogenase isoenzymes from human erythrocytes in free state and in the presence of serotonin have been studied by means of gel chromatography, electrophoresis, IR-spectrophotometry and by the method of definition of catalytic activity. UV-light influence induces photoinactivation of erythrocyte's LDH, while its inhibitory effect intensifies with the increase of irradiation dose. The complicated character of changes in electrophoretic mobility and percentage content of isoenzymes LDH-1, LDH-2, LDH-3 under the influence of UV-rays testifies that the decrease of total enzyme activity of these isoforms in connected with their different photosensitiveness and represents the result of many-staged process which is characterized both by the consistent and parallel proceeding of its individual photochemical reactions. A pronounced photoprotective effect of serotonin towards the molecules of erythrocytic LDH isoenzymes has been discovered. It seems to be caused by formation of enzyme--biogenous amine complex affecting the secondary protein structure.