Two structural types of mercury reductases and possible ways of their evolution

Abstract
Structural differences have been revealed among mercury reductases of immunologically unrelated types from Gram‐positive bacteria: enzymes of one immunological type have a molecular mass of 62–69 kDa and seem to contain an N‐terminal extension of 5–15 kDa, which is easily cleaved by trypsin and chymotrypsin; enzymes of the other immunological type have a molecular mass of 52–57 kDa and are resistant to proteolysis. The existence of at least two different lines in the evolution of mercury reductases is surmised.