OHCU decarboxylase activity of TTL. Uricase was pre-incubated with uric acid to produce 5-HIU. When the absorbance measured at 257 nm reached its maximum (in approximately 60 seconds), TTL was added. Since in presence of TTL, 5-HIU is completely degraded in 100 seconds (from 60 to 160 seconds; see Fig. 6), the absorbance decay after this point (marked with a dash line) measured at 257 nm is only due to OHCU degradation. The equivalent control for the spontaneous degradation of OHCU was built from Fig. 7 (in this case the time was marked in the upper X axis). Starting from the dashed line, both X axes show the same time period of 390 seconds (160 to 550 seconds and 2700 to 3090 seconds).