Nitric oxide-mediated heme oxidation and selective beta-globin nitrosationof hemoglobin from normal and sickle erythrocytes

Nitric oxide (NO) has been reported to modulate the oxygen affinity of bloo d from sickle cell patients (SS), but not that of normal adult blood (AA), with little or no heme oxidation, However, we had found that the NO donor c ompounds 2-(N,N-diethylamino)-diazenolate-2-oxide (DEANO) and S-nitrosocyst eine (CysNO) caused increased oxygen affinity of red cells from both AA and SS individuals and also caused significant methemoglobin (metHb) formation . Rapid kinetic experiments in which HbA(0), AA, or SS erythrocytes were mi xed with CysNO or DEANO showed biphasic time courses indicative of initial heme oxidation followed by reductive heme nitrosylation, respectively. Hemo lysates treated with CysNO showed by electrospray mass spectrometry a peak corresponding to a 29 mass unit increase (consistent with NO binding) of bo th the beta(A) and beta(S) chains but not of the alpha chains, Therapeutic use of NO in sickle cell disease may ultimately require further optimizatio n of these competing reactions, i.e., heme reactivity (nitrosylation or oxi dation) versus direct S-nitrosation of hemoglobin on the P-globin, (C) 2000 Academic Press.