An enzyme from the earthworm Eisenia fetida is not only a protease but also a deoxyribonuclease.

Abstract The earthworm enzyme Eisenia fetida Protease-III-1 ( Ef P-III-1) is known as a trypsin-like protease which is localized in the alimentary canal of the earthworm. Here, we show that Ef P-III-1 also acts as a novel deoxyribonuclease. Unlike most DNases, this earthworm enzyme recognizes 5′-phosphate dsDNA (5′P DNA) and degrades it without sequence specificity, but does not recognize 5′OH DNA. As is the case for most DNases, Mg 2+ was observed to markedly enhance the DNase activity of Ef P-III-1. Whether the earthworm enzyme functioned as a DNase or as a protease depended on the pH values of the enzyme solution. The protein acted as a protease under alkaline conditions whereas it exhibited DNase activity under acid conditions. At pH 7.0, the enzyme could work as either a DNase or a protease. Given the complex living environment of the earthworm, this dual function of Ef P-III-1 may play an important role in the alimentary digestion of the earthworm.