title: Metallothionein biodegradation in rat hepatoma cells: a compartmental analysis aided 35S-radiotracer study.
abstract: Disappearance rates, synthesis and biodegradation of rat HTC cell metallothioneins (MT) were examined by measurements of [35S]MT, and expressed by their rate constants in experiments carried out under steady-state conditions, with physiological doses of zinc and copper. Overall rates of disappearance of [35S]MT did not obey first-order kinetics, apparently due to the presence of chemically and/or spatially distinguishable MT (sub)pools. Application of compartmental analysis yielded results indicating that: (a) MT in copper-treated cells is stabler than MT in zinc-treated cells, (b) apparent half-lives for MT disappearance are 22-25 h under the conditions as described, (c) addition of 0.1 mM chloroquine reduces the overall rate of MT disappearance by 25%, (d) total MT should be regarded as significantly consisting of at least two MT sub-forms, i.e., Apo-MT and M-MT and/or cytosolic MT and lysosomal MT, each being depleted and replenished at different rates, (e) mean half-lives for total MT, based on actual degradation rates, were 3-7 h, (f) addition of 0.1 mM chloroquine resulted in both increased synthesis and increased degradation of non-lysosomal MT, the latter probably due to free amino acid depletion in the cells, and (g) MT behaviour may be best examined by combination of tracer experiments (35S-labeled amino acids), simultaneous determination of MT levels in all (sub)MT pools, and application of compartmental analysis.
authors.affiliation: Department of Radiochemistry, Delft University of Technology, Netherlands.
authors.forename: O M
authors.initials: OM
authors.lastname: Steinebach
authors.forename: B T
authors.initials: BT
authors.lastname: Wolterbeek
mesh_terms: D000818:Animals; D001692:Biological Transport; D001711:Biotransformation; D002470:Cell Survival / Q000187:drug effects; D002738:Chloroquine / Q000494:pharmacology; D003300:Copper / Q000378:metabolism / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D007700:Kinetics; D008114:Liver Neoplasms, Experimental / Q000378:metabolism*; D008433:Mathematics; D008668:Metallothionein / Q000378:metabolism*; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism; D011865:Radioisotope Dilution Technique; D051381:Rats; D013347:Subcellular Fractions / Q000378:metabolism; D013462:Sulfur Radioisotopes; D013997:Time Factors; D014407:Tumor Cells, Cultured; D015032:Zinc / Q000378:metabolism / Q000494:pharmacology
chemical_list: D013462:Sulfur Radioisotopes; D003300:Copper; D002738:Chloroquine; D008668:Metallothionein; D015032:Zinc; D011188:Potassium