Mung bean nuclease: mode of action and specificity vs synthetic esters of 3'-nucleotides.

Mung bean nuclease hydrolyzes synthetic esters of 3'-nucleotides to nucleosides and phosphate esters; esters of 2'-nucleotides, and 2'--> 5' internucleotide linkages, are resistant. Esters of ribonucleotides are cleaved at 100-fold the rate for deoxyribonucleotides, the increased rate being due to presence of the 2'-hydroxyl and not to differences in conformation. Introduction of a 5'-substituent leads to a 3-fold increase in rate. The rates of hydrolysis vary up to 10-fold with the nature of the base, in the order adenine > hypoxanthine > uracil; and up to 6-fold with the nature of the ester radical. This form of cleavage of esters of 3'-nucleotides is also characteristic for nuclease-3'-nucleotidase activities from potato tubers and wheat, suggesting that one type of enzyme is responsible for all these activities.