Methyl acetyl phosphate, a new type of antisickling agent: site-specific acetylating agent toward the 2,3-DPG binding site in hemoglobin S.

Methyl acetyl phosphate inhibits the sickling of erythrocytes in vitro. Its mechanism of action is through the selective acetylation of some of the amino groups at the 2,3-diphosphoglycerate (2,3-DPG) binding site of the hemoglobin molecule. Only 3 of a total 24 amino groups per alpha beta-dimer of hemoglobin are reactive. These groups are Val-1, Lys-82, and Lys-144 on the beta-chain of hemoglobin. None of the groups on the alpha-chain are acetylated. Acetylated hemoglobin S has an increased solubility as well as a reduced ability to bind to 2,3-DPG. Methyl acetyl phosphate is able to penetrate the erythrocyte membrane and successfully acetylate intracellular hemoglobin S without causing cell lysis. Sickle erythrocytes treated with methyl acetyl phosphate maintain an oxy-like profile of cell density distribution in a phthalate ester gradient. The oxygen binding property of erythrocytes after the treatment with methyl acetyl phosphate is not changed significantly from that of untreated cells. Our in vitro results indicate that further preclinical testing of methyl acetyl phosphate in sickle cell anemia is warranted.