Importance of storage conditions for the stability of zinc- and cadmium-induced metallothionein.
We examined the storage stability of metallothionein (MT), a cysteine-rich protein that has diagnostic potential as a cancer marker and in the assessment of Zn status and heavy-metal toxicity. MT was rapidly degraded in samples of rat whole liver at -20 degrees C or -70 degrees C. MT in supernatants from heat-treated rat liver homogenates stored as 1:5 dilutions of liver from Zn- or Cd-induced rats were stable (recovery >98%) for 100 d at temperatures of -70 degrees C and -196 degrees C but not at -20 degrees C, regardless of the presence of dithiothreitol (DTT) or argon. The variability of MT measurement by the 109Cd-hemoglobin affinity assay was however greatest in samples from Zn-induced rats stored without DTT. The integrity of the MT protein in supernatants of heat-treated homogenates stored for 100 d was demonstrated by Sephadex G-75 chromatography. When heat-treated supernatants were stored as dilute solutions (1:125 of liver), MT was unstable regardless of treatment or storage temperature. Our findings show that liver MT is stable for at least 4 mo as a supernatant of a heat-treated homogenate (1:5 dilution of liver) when stored at or below -70 degrees C and in the presence of DTT.
Coyle
P
P
Division of Clinical Biochemistry, Institute of Medical and Veterinary Science, Adelaide, SA, Australia.
Hubert
C A
CA
Philcox
J C
JC
Rofe
A M
AM
D000818:Animals; D001128:Argon / Q000494:pharmacology; D002104:Cadmium / Q000737:chemistry*; D002845:Chromatography; D003911:Dextrans / Q000737:chemistry; D004229:Dithiothreitol / Q000494:pharmacology; D004355:Drug Stability; D004356:Drug Storage; D006454:Hemoglobins / Q000378:metabolism; D006358:Hot Temperature; D008099:Liver / Q000378:metabolism; D008297:Male; D008668:Metallothionein / Q000737:chemistry*; D051381:Rats; D013696:Temperature; D013997:Time Factors; D015032:Zinc / Q000737:chemistry*
D003911:Dextrans; D006454:Hemoglobins; D002104:Cadmium; D001128:Argon; C025614:sephadex; D008668:Metallothionein; D015032:Zinc; D004229:Dithiothreitol