Three isoforms of metallothionein protein induced with Zinc were isolated and purified from housefly larvae, Musca domestica, by gel filtration on Sephadex G-75, G-25 and anion exchange on DEAE-52 chromatography. Among them, one was found to possess antibacterial activity, and was further characterized by SDS-polyacrylamide gel electrophoresis, sulphydryl group determination, enzyme hydrolysis, and spectra property. Our results showed that the novel protein has the characteristics of heat-stable, low-molecular weight (6 kDa), rich-cysteine (approximately 12 cysteine residues in one molecule), metal affinity, and antibacterial activity. This paper was the first to report that metallothionein had antibacterial activity. We expect that this characteristic would give some help to investigate definite physiological functions of metallothionein.

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