PERSISTENT INHIBITION OF CELL RESPIRATION BY NITRIC-OXIDE - CRUCIAL ROLE OF S-NITROSYLATION OF MITOCHONDRIAL COMPLEX-I AND PROTECTIVE ACTION OF GLUTATHIONE

Both reversible and irreversible inhibition of mitochondrial respirati on have been reported following the generation of nitric oxide (NO) by cells, Using J774 cells, we have studied the effect of long-term expo sure to NO on different enzymes of the respiratory chain, Our results show that, although NO inhibits complex IV in a way that is always rev ersible, prolonged exposure to NO results in a gradual and persistent inhibition of complex I that is concomitant with a reduction in the in tracellular concentration of reduced glutathione. This inhibition appe ars to result from S-nitrosylation of critical thiols in the enzyme co mplex because it can be immediately reversed by exposing the cells to high intensity light or by replenishment of intracellular reduced glut athione. Furthermore, decreasing the concentration of reduced glutathi one accelerates the process of persistent inhibition. Our results sugg est that, although NO may regulate cell respiration physiologically by its action on complex IV, long-term exposure to NO leads to persisten t inhibition of complex I and potentially to cell pathology.