Generation of peptides by human erythrocytes: facts and artifacts

Previously reported data on peptide composition of human erythrocyte lysate were obtained under conditions that did not exclude proteolytic degradation of hemoglobin in the process of peptide isolation. Comparative chromatographic analysis of the diluted erythrocyte lysate incubated in acidic conditions with or without proteolytic enzyme inhibitors showed that several peptides earlier identified as intraerythrocyte ones in fact result from hemoglobin degradation by erythrocyte acidic protease(s) during incubation of the lysate. A rational scheme excluding postlysis proteolysis was developed for isolation of peptide fraction. Further analysis resulted in determination of structure and content of about 50 endogenous intraerythrocyte hemoglobin fragments. A primary endopeptidase splitting of alpha- and beta-globin chains followed by consecutive exopeptidase trimming of primary fragments is suggested as a degradation mechanism. The intraerythrocyte peptides were shown to differ from peptides excreted by the erythrocytes to the extracellular medium in the primary culture. It was also found that intraerythrocyte peptides cannot play the role of precursors of hemoglobin fragments present in tissue extracts.