Binding of TAT-Gel to heparin sepharose beads and protamine-triggered release. FITC-labeled TAT-Gel was loaded onto heparin beads (Heparin HyperD® M, Pall Corporation, Port Washington, NY; 50% (v/v) in PBS) and incubated up to 24 h at 37°C in rat plasma. At intended time points (0, 1 h, 4 h, 6 h, 12 h and 24 h), beads (N = 3 per time point) were washed, and the bound FITC-labeled TAT-Gel remaining on the beads’ surface were eluted with 2 M NaCl solution. Protamine-triggered release of TAT-Gel was tested by addition of excessive protamine (1 mg) to a group of heparin beads loaded with FITC-labeled TAT-Gel and incubation for 30 min at 37°C. The fluorescence intensities of all the eluents were measured and the bound fraction of FITC-labeled TAT-Gel on the heparin bead (%) for each test tube was calculated by dividing the fluorescence intensity of the eluent by the mean fluorescence intensity of the control group's eluents. Statistical significant differences in the bound fractions of TAT-Gel among the groups were compared by 1-way ANOVA with Tukey's multiple comparison test as the post hoc test using Prism software (GraphPad). *** P < 0.0001. (TAT-Gel: recombinant TAT-gelonin fusion protein)