J. Biochem, 2004, Vol. 135, No. 6 713-719
© 2004 The Japanese Biochemical Society
BIOCHEMISTRY |
Low pH Facilitates Uptake of Proteins by Cells through a Non-Endocytic Pathway
1 Department of Biochemistry 2, 2 Department of Immunology, and 3 Biological Laboratory, Faculty of Medicine, University of Yamanashi, Nakakoma, Yamanashi 409-3898; and 4 the Institute for Biomolecular Science, Gakushuin University, Tokyo 171-8588
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 (Mr) 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°C and internalized ß-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.
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