Mung bean nuclease I. 6. Physical, chemical, and catalytic properties

Publisher Website
Google Scholar
Abstract
A simplified purification procedure for mung bean nuclease was developed yielding a stable enzyme that is homogeneous in regards to shape and size. The nuclease is a glycoprotein consisting of 29% carbohydrate by wt. It has a MW of 39,000 as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The enzyme contains 1 sulfhydryl group and 3 disulfide bonds/molecule. It has a high content (12.6 mol %) of aromatic residues. Approximately 70% of the enyzme molecules contain a peptide bond cleavage at a single region in the protein. The 2 polypeptides, 25,000 and 15,000 daltons, are covalently linked by a disulfide bond(s). The cleaved and intact forms of the enzyme are equally active in the hydrolysis of the phosphate ester linkages in either DNA, RNA or AMP. The enzymatic activity of mung bean nuclease can be stabilized at pH 5 in the presence of 0.1 mM zinc acetate, 1.0 mM cysteine and 0.001% Triton X-100. The enzyme can be inactivated and reactivated by the removal and readdition of Zn2+ or sulfhydryl compounds.