The effect of pH and lysosomal extract on rat liver metallothionein (Cd-thionein)

Was studied in vitro. The(109)Cd-labeled protein was isolated by gel filtration and incubated with a lysosomal extract from the same source. No degradation was seen when the pH of the incubation medium was 5 or higher, whereas the degradation of Cd-thionein was completed in 2 h at a pH of 4.5. Dissociation of Cd(2+) from thionein, which takes place to a fair extent at a pH below 5, appears necessary before the enzymatic breakdown of the thionein moiety can take place.