Effect of mercurial compounds on structure-linked latency of lysosomal hydrolases

Abstract

1. A partially purified lysosomal preparation was obtained from adult mouse livers by sucrose-density-gradient centrifugation of a large-granule fraction. 2. This lysosome-enriched subfraction was contaminated approx. 10% by mitochondrial cytochrome c oxidase and malate dehydrogenase. 3. Free acid phosphohydrolase and β-glucuronidase contributed less than 10% of the total (Triton X-100-solubilized) activity in contrast with approx. 30% free N-acetyl-β-d-glucosaminidase when assayed in an iso-osmotic incubation system. 4. Exposure of the lysosomal preparation to inorganic Hg²⁺ ions and organic mercurials (p-chloromercuribenzoate, phenylmercuric acetate) induced an irreversible loss of structure-linked latency with resulting enzyme activation. 5. Maximal activation was related to log [Hg²⁺] and pH. The response was all-or-none for individual particles; the dose–response curve portrayed the variation in particle resistance within the lysosomal population. 6. l-Cysteine and GSH totally prevented Hg²⁺ ion-induced hydrolase activation. Ascorbate provided approx. 50% protection. 7. The three lysosomal hydrolases were differentially activated at constant [Hg²⁺], suggesting a different pattern of binding, unique for each enzyme studied.