Binding uptake and degradation of antithrombin III · protease complexes by cultured corneal endothelial cells

Naphtali Savion*, Nahid Farzame

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Interaction of 125I-labeled human antithrombin III (125I-AT III) · protease complexes with bovine corneal endothelial cells has been studied in tissue culture. 125I-AT III does not bind to endothelial cells, but its complexes with either thrombin or trypsin bind specifically to the cultures. The binding of 125I-AT III · protease complexes is not via the moiety of the free antithrombin III (AT III) or the free protease, since neither AT III nor thrombin compete on the binding of 125I-AT III · thrombin complexes. Only unlabeled AT III · thrombin complexes compete on the binding of the iodinated ligand. 125I-AT III · trypsin complexes bind with a KD of 1.4 × 10-7 M to high affinity-binding sites present on the cell surface of corneal endothelial cells. Saturation of binding to the cell surface is observed at a concentration of 2.5 × 10-7 M 125I-AT III · trypsin complexes and the number of binding sites per cell is about 4 × 104. The cell surface binding reaches a maximum by 15 min and then decreases with time. The cells, when incubated at 37 °C, appear to internalize the bound complexes by adsorptive endocytosis which proceeds at a rate of 0.5-0.8 pmole/1 × 106 cells/h. The internalization process of 125I-AT III · protease complexes is saturated at a concentration of 2.5 × 10-7 M. Since the cells release 125I-labeled material into the extracellular media which cannot be precipitated by trichloroacetic acid (TCA), it probably represents degradation of 125I-AT III · protease complexes into small fragments at a linear rate of about 0.5 pmole/1 × 106 cells/h. The described process of AT III · protease complexes binding, internalization and subsequent degradation by corneal endothelial cells may represent a clearing mechanism for extracellular AT III · protease complexes formed under pathological conditions.

Original languageEnglish
Pages (from-to)50-60
Number of pages11
JournalExperimental Cell Research
Volume153
Issue number1
DOIs
StatePublished - Jul 1984

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