Cadmium in rat kidney subcellular particles after injection of cadmium-metallothionein

Distribution and forms of cadmium in the subcellular fraction after an intraperitoneal injection of Cd-metallothionein (Cd-MT) were studied to trace the metabolic fate of metallothionein in the kidney. Cd-containing components from the mitochondria, lysosomes and cytoplasm were gel filtered on Sephadex G-75 at 4, 24 and 72 hr after injection of Cd-MT. The chromatographic distribution patterns of cadmium were different among these three fractions and changed with time. At 4 hr a moderate amount of cadmium in the cytoplasm, and most of the cadmium in the lysosomes and mitochondria was bound to high molecular weight (HMW) proteins eluted in the void volume. At 24 hr almost all the cadmium in the cytoplasm became bound to metallothionein fraction, while most of the cadmium in the mitochondria and lysosomes was still bound to the HMW proteins. Since in the in vitro experiment the cadmium ions were nonspecifically bound to the HMW proteins, the longer term existence of cadmium in the HMW proteins in the lysosomes than in the cytoplasm after injection of Cd-MT, suggest that Cd-MT is degraded in the lysosomes, and that the inorganic cadmium ions liberated from the degraded proteins are bound to the HMW proteins. The present paper deals with the involvement of the lysosomes in the in vivo degradation of Cd-MT.