Identification and characterization of metallothionein III (growth inhibitory factor) from porcine brain

Porcine metallothionein III (MTIII) was isolated from brain tissue by the combination of gel filtration and anion-exchange chromatographies. The identity of MTIII was confirmed by comparing the chromatographic characteristics to other MT isoforms isolated from porcine liver. Porcine MTIII has a low molecular weight and a pl of 4.1. This protein contains both zinc and copper, and the zinc can be replaced by cadmium. Using reverse transcriptase-polymerase chain reaction, a 0.2 kb DNA fragment can be amplified from the porcine brain mRNA. This DNA fragment was demonstrated to contain MTIII coding region after cloning and sequencing. The revealed DNA sequence can be translated into 68 amino acids and shows a common structural characteristic of MTIII from other species. Northern blot analysis indicated that MTIII and mRNA is expressed in every specified region of the porcine brain examined here.