Synthesis of the minor fetal hemoglobin Fic in colonies of erythropoietic precursors isolated from human umbilical cord blood

Human red cell acetyltransferase

Acetyltransferase was isolated by histone-Sepharose affinity chromatography from human cord blood red cells. The enzyme was detected only in very young red cells. The semipurified enzyme and [14C]acetyl-CoA were used to acetylate isolated Hb F tetramer and alpha and gamma subunits. The in vitro acetylated products were characterized by globin chain separation by CM-cellulose chromatography and tryptic peptide analysis by reverse-phase HPLC. Acetylation of both the gamma-chains and the alpha-chains could occur within the Hb F tetramer. Acetylation also could take place on intact subunits. It appears that some Hb FIC could be formed in the cells by utilizing Hb F or free gamma-chains as acetylation substrate.

Human fetal hemoglobin synthesis and its NH2-terminal acetylation in a rabbit reticulocyte lysate translational system

The biosynthesis of the acetylated (Hb FIc) and the non-acetylated (Hb F0) human fetal hemoglobin components has been examined in a cell-free translational system. The poly(A)-RNA was isolated from umbilical cord blood samples and translated in the heterologous translational system derived from rabbit reticulocyte lysates in the presence of labeled amino acid(s) or acetyl-CoA. The amount of each hemoglobin or globin chain made in the system was determined by separating the synthesis products by cation-exchange chromatographic methods. The in vitro synthesis ratios were close to the FIc/Ftotal values of the respective hemolysates. The same conclusion could be reached by determining the specific activity ratios of Hb FIc/Hb F0. Co-migration of radioactivity peaks with absorbance peaks indicated the synthesis of that hemoglobin or globin chain. Confirmation of the synthesis of true gamma 0 and gamma Ic was accomplished by high-pressure liquid chromatographic separation of 3H-labeled tryptic peptides. Each peptide corresponded well with the radioactivity peak. Labeled acetyl-group incorporation into Hb FIc and gamma IcT-1 provided direct evidence for acetylation of gamma chains in Hb FIc. The data indicate that the mRNA itself dictates whether a protein is acetylated and, if so, to what extent. The control appears to be not unique to the human red cell system.

Glycosylated and acetylated hemoglobins in relation to gestational age and red cell age

Cord blood samples were obtained at delivery from women at gestational periods of 30 to 36 weeks (preterm) and from a control group at 40 weeks of gestational age (term). Total glycosylated hemoglobin (GHb) was determined by affinity chromatography and the percentages of the minor Hbs FIa+b and FIc (of total Hb F) were determined by Bio-Rex 70 chromatography in whole blood samples and in red cell populations separated by Dextran 40 density gradient centrifugation. The absolute levels and the increase due to red cell aging of GHb, Hb FIa+b and Hb FIc were significantly reduced in the preterm samples compared to the term samples indicating decreased glycosylation in preterm fetus. When the nonglycosylated Hbs from term and preterm newborns were separated by Bio-Rex 70 chromatography after removal of the GHb by affinity chromatography, the acetylated form of Hb FIc also showed an increase with red cell aging indicating posttranslational enzymatic or nonenzymatic acetylation of Hb F during the entire life span of red cells. Moreover, as with GHb, the acetylated Hb was also decreased in the preterm newborns.