Isolation and characterization of metallothionein which is highly concentrated in newborn rat liver.

The hepatic concentration of a low molecular weight, metal-binding protein in lto 4-day-old rats is 20 times that in 70-day-old adults. Biochemical purifications were performed to characterize this metal-binding protein in the liver of lto 4-day-old rats. Gel filtration of hepatic cytosol on Sephadex G-75 demonstrated that the major Zn-containing fraction of newborns had a relative elution volume and low absorbance at 280 nm, similar to the metallothionein fraction of Zn-treated adult rats. These fractions were further purified by DEAE-Sephadex A-25 chromatography and two major subfractions (MT-A and MT-B) were obtained from both the newborns and Zn-treated adults, with the corresponding subfractions eluted in buffer of similar conductivity. MT-A and MT-B of newborns also exhibited mobilities on polyacrylamide gel electrophoresis similar to the corresponding subfractions from Zntreated adults. Both subfractions from the newborns had an abundance of half-cystine and a deficiency in most aromatic amino acids which are characteristics of metallothionein. Therefore, according to all of the criteria commonly used for the identification of metallothionein, these data demonstrate that the metal-binding protein which is highly concentrated in newborn liver is metallothionein. The variation of the concentration of hepatic and renal metallothionein with age was also determined. The hepatic concentration peaks at 1 to 4 days of age and falls rapidly after that, reaching the adult level at 28 days of age. However, the renal concentration showed no variation with age.