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, ZnSO4, Zn(CH3CO2)2 or Zn(NO3)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 ZnSO4, Zn(CH3CO2)2, Zn(NO3)2, or zinc-thionein resulted in reactivation of the apo-enzymes. With apo-aldolase zinc-thionein gave 100/o reactivation within 30min. Reactivation by ZnSO4 and Zn(CH3CO2)2 was complete and instantaneous. Zinc-thionein was somewhat better than Zn(NO3)2 in completely reactivating apo-thermolysin. With apo-(alkaline phosphatase) 43% reactivation was obtained with Zn(CH3CO2)2 and 18% with zinc-thionein. With apo-(carbonic anhydrase) zinc-thionein was better than ZnSO4, Zn(CH3CO2)2 or Zn(NO3)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 + chelatori }. 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.

This study shows that in vivo [18F]FLT kinetics depend on TK1 protein expression. ATP may be important in realising this effect. Thus, [18F]FLT-PET has the potential to yield specific information on tumour proliferation in diagnostic imaging and therapy monitoring.

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The distribution of [11C]DACA and its radiolabeled metabolites was observed in a variety of tumors and normal tissues. In the presence of unlabeled DACA, pharmacokinetics were altered in myocardium, spleen, and tumors. These data have implications for predicting activity and toxicity of DACA and support the use of PET early in drug development.