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Flow kinetics of mouse histocompatibility antigens
Major histocompatibility antigens of the mouse (H-2 antigens) are found on a variety of different cell types and constitute a class of integral membrane-bound glycoproteins involved in tissue graft rejection and immune surveillance. We used monospecific alloantibodies directed against mouse H-2 antigens and standard pulse-chase technique to investigate the flow kinetics of delivery of newly synthesized membrane constituents to the cell surface. [35S]Methionine was injected intraperitoneally, and, after a chase with unlabeled methionine, livers were excised and fractionated into endoplasmic reticulum, Golgi apparatus, and plasma membrane fractions. Label first appeared in H-2 antigens located within the endoplasmic reticulum. Maximum specific activity observed between 5-7 min after injection of label was followed by a rapid loss of label. H-2 antigens of Golgi apparatus also were labeled early. Peak specific activity observed 15-25 min after injection of label was again followed by rapid loss of label. H-2 antigens of the plasma membrane were labeled last and appeared to accumulate radioactivity with no evidence of rapid turnover. These results provide evidence for a precursor-product relationship between H-2 antigens located within the cell on membranes of endoplasmic reticulum and Golgi apparatus and those on the plasma membrane. Flow of individual membrane-bound glycoproteins from their sites of synthesis and insertion into the membrane of the endoplasmic reticulum to the plasma membrane through the Golgi apparatus is indicated.
Major histocompatibility antigens of the mouse (H-2 antigens) are found on a variety of different cell types and constitute a class of integral membrane-bound glycoproteins involved in tissue graft rejection and immune surveillance. We used monospecific alloantibodies directed against mouse H-2 antigens and standard pulse-chase technique to investigate the flow kinetics of delivery of newly synthesized membrane constituents to the cell surface. [35S]Methionine was injected intraperitoneally, and, after a chase with unlabeled methionine, livers were excised and fractionated into endoplasmic reticulum, Golgi apparatus, and plasma membrane fractions. Label first appeared in H-2 antigens located within the endoplasmic reticulum. Maximum specific activity observed between 5-7 min after injection of label was followed by a rapid loss of label. H-2 antigens of Golgi apparatus also were labeled early. Peak specific activity observed 15-25 min after injection of label was again followed by rapid loss of label. H-2 antigens of the plasma membrane were labeled last and appeared to accumulate radioactivity with no evidence of rapid turnover. These results provide evidence for a precursor-product relationship between H-2 antigens located within the cell on membranes of endoplasmic reticulum and Golgi apparatus and those on the plasma membrane. Flow of individual membrane-bound glycoproteins from their sites of synthesis and insertion into the membrane of the endoplasmic reticulum to the plasma membrane through the Golgi apparatus is indicated.