Quantitative assessment of the amount and the activity of trypsin associated with trypsinized cells

The present investigation has demonstrated that when cell layers are trypsinized with 125I-trypsin and washed under strictly standardized conditions, the amount of trypsin which remains associated with the cell suspension can be accurately determined. This amount is more than 10 times greater than would be expected from dilution only and is dependent on the density of the cell layers. On plating of the cells, less than 10% of the carry-over trypsin remains associated with the cells and suggestive evidence for a mainly intracellular localization was obtained with a quantitative immunoperoxidase technique. This carry-over trypsin was further shown to maintain proteolytic activity by its ability to remove significant amounts of macromolecular material from a cell layer prelabeled with 3H-Leucine.