title: Low pH facilitates uptake of proteins by cells through a non-endocytic pathway.
abstract: We previously noted that bovine apolipoprotein A-II (apoA-II) had a bactericidal effect causing morphological changes in the cytoplasm. To determine whether and how apoA-II and apoA-I, which have acidic isoelectric points (pIs), enter cells, we determined the rates of uptake of FITC-labeled proteins by fibroblast cells and found that they entered cells more easily at low pH than at neutral pH under conditions where endocytosis was inhibited. The enhanced uptake of proteins at low pH was also observed for other proteins examined regardless of the molecular weight (M(r)) or pI in a time-dependent manner, although the efficiency of uptake varied among the proteins. Furthermore, a pH gradient was shown to be the main driving force for the translocation. As cells were viable above pH 4 for 2 h at 4 degrees C and internalized beta-galactosidase was active under these conditions, we suggest that this procedure is applicable to the injection of proteins into cells without the use of an apparatus such as a microinjector.
authors.affiliation: Department of Biochemistry 2, Faculty of Medicine, University of Yamanashi, Nakakoma, Yamanashi 409-3898, Japan.
authors.forename: Mitsuyoshi
authors.initials: M
authors.lastname: Motizuki
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Takei
authors.forename: Kachio
authors.initials: K
authors.lastname: Tasaka
authors.forename: Sadaki
authors.initials: S
authors.lastname: Yokota
authors.forename: Shuichi
authors.initials: S
authors.lastname: Kojima
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Haga
authors.forename: Kunio
authors.initials: K
authors.lastname: Tsurugi
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001053:Apolipoproteins / Q000378:metabolism*; D002417:Cattle; D002470:Cell Survival; D004705:Endocytosis; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008807:Mice, Inbred BALB C; D021381:Protein Transport; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D001053:Apolipoproteins; D001616:beta-Galactosidase