The amino terminal acetylation of cat globin chains and their tryptic peptides.

Cat blood contains two major hemoglobins, HbA and HbB, both of which are synthesized within the same red cell. They contain identical alpha chains but different beta chains. HbB is somewhat unusual in that it contains beta chains that are modified by N alpha-acetylation. Although the selective amino terminal acetylation of the beta chain of cat HbB occurs during nascent peptide chain growth, it can also occur after completion of globin chain synthesis and its assembly into hemoglobin. However, the latter process is not as efficient as the former, and it occurs non-enzymatically. Two peptides in a mixture of tryptic peptides from cat HbA and non-acetylated cat HbB contain serine at their amino terminus. One is the octapeptide, non-acetylated B- beta T-1, and the other is the tetrapeptide, alpha T-2, derived from both HbA and HbB. We provide evidence here that in a mixture of soluble tryptic peptides, acetylation of alpha T-2 takes place in the presence of acetyl-CoA and ribosomal acetyltransferase at pH 7.0. The amino terminal acetylation requires the presence of an acetyltransferase.