Inhibition of a reductive function of the plasma membrane by bacitracin and antibodies against protein disulfide-isomerase.
Evidence had been provided that a disulfide-linked [125I]iodotyramine/poly(D-lysine) conjugate was reductively cleaved when bound nonspecifically to the surface of Chinese hamster ovary (CHO) cells and that this cleavage was abolished by membrane-impermeant sulfhydryl blockers. The same blockers were subsequently found to inhibit the cytotoxicity of diphtheria toxin, a disulfide-linked heterodimer that binds to a specific surface receptor and must undergo chain separation to exert its cytotoxicity. This suggested that the disulfides of both macromolecules might be cleaved by a thiol-disulfide interchange reaction, possibly mediated by protein disulfide-isomerase (PDI, EC 5.3.4.1). We tested whether inhibitors of PDI--in particular, bacitracin and anti-PDI antibodies--might mimic the two effects of sulfhydryl blockers. Both bacitracin and anti-PDI antibodies were effective in inhibiting both reductive processes. This strongly suggests that the disulfide cleavage in the two membrane-bound macromolecules is mediated by PDI and that this enzyme, besides its known retention in the endoplasmic reticulum, must also be exposed at the plasma membrane. This paper points to other potentially important disulfide reductions that might be catalyzed by surface-associated PDI. It thereby broadens the known functions of an enzyme already known for its multifunctional properties.
Mandel
R
R
Department of Pathology, Boston University School of Medicine, MA 02118.
Ryser
H J
HJ
Ghani
F
F
Wu
M
M
Peak
D
D
D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D001414:Bacitracin / Q000494:pharmacology*; D016466:CHO Cells; D002417:Cattle; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D004167:Diphtheria Toxin / Q000494:pharmacology; D004220:Disulfides / Q000378:metabolism; D004228:Dithionitrobenzoic Acid / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D007535:Isomerases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008969:Molecular Sequence Data; D019704:Protein Disulfide-Isomerases
D000911:Antibodies, Monoclonal; D004167:Diphtheria Toxin; D004220:Disulfides; D007328:Insulin; D001414:Bacitracin; D002731:4-Chloromercuribenzenesulfonate; D004228:Dithionitrobenzoic Acid; D007535:Isomerases; D019704:Protein Disulfide-Isomerases