Hepatic copper overload inherited as an autosomal recessive trait in Bedlington Terriers is characterized by the presence of hepatocellular lysosomal granules of unusually high specific gravity and electron density which contain at least two thirds of the total hepatic copper.
Fractionation of homogenates of liver from such affected Bedlington Terriers yielded a low-speed pellet which contained the lysosomal granules. This fraction was used for isolation of a copperbinding protein by alkaline-reduction, solubilization, fractional acetone precipitation, and gel filtration. The purified protein yielded a single band on polyacrylamide gel electrophoresis and resembled other metallothioneins in containing 15 cysteine residues and 7 to 8 atoms of copper (but no zinc) per 54 amino acid residues. No methionine, histidine, or any aromatic amino acid was present. The accumulation of this lysosomal copper protein appears to be related to the primary genetic defect which underlies the hepatic copper toxicosis of the Bedlington Terrier.
An inherited metabolic abnormality prevalent in Bedlington Terriers in the United States results in a progressive accumulation of copper associated with pathological changes in hepatic function and structure (1-4). Most of this copper is contained in distinctive lysosomal granules which stand out as hepatocellular dark bodies in histologic and electron microscopic sections. We have isolated and characterized the lysosomal copper liver protein (LyCuLP) which sequesters the copper in these lysoso-ma1 granules in beginning our study of the pathogenesis of this form of hepatic copper toxicosis.
Methods
Liver specimens were obtained at surgery or necropsy. Hepatic copper concentrations of two unaffected Bedlington Terriers and of six dogs of other breeding used in the study ranged from 142 to 268 pg per gm dry tissue. The livers of the six affected Bedlington Terriers showed the presence of the characteristic hepatocellular dense granules in histologic sections (1) and hepatic copper concentrations which ranged from 3,865 to 5,550 pg per gm dry tissue.