DNA METHYLATION BY WHEAT CYTOSINE DNA METHYLTRANSFERASE - MODULATION BY PROTEASE INHIBITOR E-64

Cytosine DNA methyltransferase isolated from wheat seedlings and purif ied in the presence of metalloprotease and serine protease inhibitors has molecular mass and specific activity equal to about 85 kDa and 250 units/mg protein, respectively. Apparent K-m for AdoMet(&) and [I](50 ) for AdoHcy values are about 6 mu M and 12 mu M, respectively. The en zyme is active in wide pH range (pH 5.5-8.5) and is inhibited by NaCl. The enzyme rapidly loses its methyltransferase activity in the absenc e of substrates. Using the cysteine protease inhibitor E-64 it has bee n shown that rapid enzyme inactivation is caused by disappearance of e ssential enzyme SH-groups but is not due to proteolytic enzyme cleavag e.