ProTPP1 diluted in aCSF was mixed with plasma from Tpp1(−/−) mice (final concentration 0.08 mg/mL TPP1, 87.5% plasma) on ice. Time courses were started by incubation at 37°C and samples frozen at the indicated times. Preparations were then activated and TPP1 activity measured and normalized to the zero timepoint. Unmodified TPP1, open circles; OX-TPP1, filled circles, DG-TPP1, gray squares. Data was fit to a single-phase exponential decay model using Graphpad Prism constraining initial values to 100% and the plateau value to 0%, yielding the following half-life estimates (with 95% confidence limits): unmodified TPP1, 8.6 (6.7–11.9) h; OX-TPP1, 3.5 (2.9–4.3) h; DG-TPP1, 1.7 (1.5–2.1) h.