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.
Jordans et al. BMC Biochemistry 2009 10:23 doi:10.1186/1471-2091-10-23