Reactivation in vitro of zinc-requiring apo-enzymes by rat liver zinc-thionein.
The ability of rat liver zinc-thionein to donate its metal to the apo-enzymes of the zinc enzymes horse liver alcohol dehydrogenase, yeast aldolase, thermolysin, Escherichia coli alkaline phosphatase and bovine erythrocyte carbonic anhydrase was investigated. Zinc-thionein was as good as, or better than, ZnSO(4), Zn(CH(3)CO(2))(2) or Zn(NO(3))(2) in donating its zinc to these apo-enzymes. Apo-(alcohol dehydrogenase) could not be reactivated by zinc salts or by zinc-thionein. Incubation of the other apo-enzymes with near-saturating amounts of zinc as ZnSO(4), Zn(CH(3)CO(2))(2), Zn(NO(3))(2), or zinc-thionein resulted in reactivation of the apo-enzymes. With apo-aldolase zinc-thionein gave 100% reactivation within 30min. Reactivation by ZnSO(4) and Zn(CH(3)CO(2))(2) was complete and instantaneous. Zinc-thionein was somewhat better than Zn(NO(3))(2) in completely reactivating apo-thermolysin. With apo-(alkaline phosphatase) 43% reactivation was obtained with Zn(CH(3)CO(2))(2) and 18% with zinc-thionein. With apo-(carbonic anhydrase) zinc-thionein was better than ZnSO(4), Zn(CH(3)CO(2))(2) or Zn(NO(3))(2), with a maximal reactivation of 54%. That zinc was really being transferred from zinc-thionein to apo-(carbonic anhydrase) was shown by the fact that 2,6-pyridine dicarboxylic acid and 1,10-phenanthroline had minimal effects on the reactivation of apo-(carbonic anhydrase) when added after the incubation {[apo-(carbonic anhydrase)+zinc thionein]+chelator}, but inhibited reactivation when added before the incubation {apo-(carbonic anhydrase)+[zinc-thionein+chelator]}. These observations support the idea that zinc-thionein can function in zinc homeostasis as a reservoir of zinc, releasing the metal to zinc-requiring metalloenzymes according to need.
D000429:Alcohol Oxidoreductases / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D001051:Apoenzymes / Q000378:metabolism*; D001059:Apoproteins / Q000378:metabolism*; D002256:Carbonic Anhydrases / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D005634:Fructose-Bisphosphate Aldolase / Q000378:metabolism; D066298:In Vitro Techniques; D008099:Liver / Q000032:analysis; D008667:Metalloproteins / Q000494:pharmacology*; D008668:Metallothionein / Q000494:pharmacology*; D051381:Rats; D013820:Thermolysin / Q000378:metabolism; D015032:Zinc
D001051:Apoenzymes; D001059:Apoproteins; D002614:Chelating Agents; D008667:Metalloproteins; D008668:Metallothionein; D000429:Alcohol Oxidoreductases; D000469:Alkaline Phosphatase; D013820:Thermolysin; D005634:Fructose-Bisphosphate Aldolase; D002256:Carbonic Anhydrases; D015032:Zinc