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

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.