Figure 6.

Cysteine cathepsins efficiency to liberate thyroxine (T₄) in vitro. Samples taken after 2h-in-vitro-degradation of Tg were assayed for their content in free thyroxine (fT₄) by ELISA. Efficiency of hormone liberation by distinct cysteine cathepsins or combinations thereof is directly correlated to the amount of fT₄. Under conditions mimicking the extracellular space, exclusively cathepsin S proved to be efficient in thyroxine liberation (A), whereas under endosomal-representative conditions all cysteine cathepsins performed equally well (B). The same holds true for conditions mimicking the lysosomal compartment, although cathepsin S was less active as reflected by lower thyroxine liberation potency as compared with e.g. cathepsin B (C). Highest amounts of fT₄ were measured for lysosomal-mimicking environments, followed by those performed under conditions simulating endosomes and the extracellular space (A-C). Values are given as mean values +/- SD.