Conformational changes induced by the addition of carbamyl phosphate to sickle cell hemoglobin

The conformational changes upon anaerobic carbamyl phosphate addition to dilute hemoglobin solutions have been studied by means of circular dichroism. Freshly prepared carbamyl phosphate stabilizes the conformation of pure deoxyhemoglobin without detectable NH2-terminal carbamylation. Addition of preincubated (i.e. partially converted to cyanate) carbamyl phosphate, however, results in such carbamylation and in the formation of the conformationally different carbamyldeoxyhemoglobin which exhibits enhanced oxygen affinity. Fresh carbamyl phosphate carbamylates hemoglobin in deoxygenated hemolysates containing erythrocyte phosphatases. Therefore the reversal of SS erythrocyte sickling by carbamyl phosphate is attributable to carbamylation by the carbamyl phosphate hydrolysis product, cyanate.