[en] The authors have been interested in human fetal hemoglobin acetylation and have focused on search of an acetyltransferase that can acetylate this hemoglobin. Cord blood ribosomal and postribosomal acetyltransferases have been partially purified by histone-Sepharose 4B affinity chromatography. Analysis of Dextran 40 fractionated cells has indicated that the enzyme is present only in reticulocytes and young erythrocytes, and mature erythrocytes are devoid of this enzyme. Enzymes prepared from the ribosomal and postribosomal sources showed similar temperature, pH, and cation dependence. In vitro acetylation of Hb F₀, Hb A₀ and native γ, β, and α chains with [¹⁴C]acetyl-CoA in the presence of these enzyme preparations failed to show any specificity to any one of the hemoglobins. No significant differences in hemoglobin acetylation were seen between the two types of enzymes. However, acetylation of Hb F₀ and γ chains did produce Hb F/sub Iac/ (Hb F/sub I/ or Hb F/sub Ic/) and γ/sub Iac/ (γ/sub I/ or γ/sub Ic/), respectively. Peptide analyses showed that the γ chain NH₂-terminus and other sites were being acetylated. Thus, site specificity is seen only when the ribosomal enzyme acts on ribosome-bound nascent chains. It is also possible that the presence of free enzyme, acetyle-CoA and potential hemoglobin substrates in the cytoplasm may lead to the formation of some Hb F/sub Iac/ and small amounts of other unidentified acetylated hemoglobins in red cells