Structural Investigations on a Peptide Regulating Hemopoiesis in vitro and in vivo

Publisher Website
Google Scholar
Abstract
Clonal growth in agar of myeloid committed stem cells (CFU-c) is inhibited by a specifically acting hemoregulatory peptide which had been isolated from human leukocytes. The inhibitory peptide is composed of aspartic acid, glutamic acid, lysine, cysteine and possibly glycine. It was [3H]carboxymethylated with [3H]iodoacetic acid. From the electrophoretic behavior of this derivative at pH 1.9 a single positive charge and a molecular mass of .apprx. 600-650 Da [daltons] could be inferred. This positive charge is lost after acetylation and is identified as the .epsilon.-amino group in the side chain of a lysine residue since the N-terminal group is a pyroglutamic residue. Electrophoresis of the native peptide at pH 6.5 reveals the presence of 3 carboxyl groups, 2 of which were localized in the N-terminal part of the molecule, while cysteine and lysine were located in the C-terminal portion. Lysine was identified as the C-terminal residue by a double labeling technique applied to the Cys-([3H]Cm)-containing fission peptide after partial hydrolysis. Uncertainties in the molecular mass determinations allow for the possible presence of a small residue without reactive side chain (glycine?) in the C-terminal portion of the molecule. The structure of the inhibitory peptide was thus determined as < Glu-(Asp/Glu)-(Asp/Glu)-Cys-(Gly?)-Lys. This structure is supported by comparison with synthetic peptides. The analog < Glu-Glu-Asp-Cys-Lys has properties which are similar to those of the natural inhibitor.