Isolation and characterization of multiple forms of malt deoxyribonuclease

A deoxyribonuclease (DNase), similar to bovine pancreatic DNase, has been isolated from germinating barley. Commerically available malt was used as source of the enzyme. The purification procedure involves (a) ammonium sulfate fractionation (45–65% saturation), (b) CM-cellulose chromatography at pH 4.7 and (c) DEAE-cellulose chromatography at pH 8. DEAE-cellulose separates the enzyme into 4 distinct forms, designed as DNases A, B, C, and D. DNase A and B may be rechromatographed on DEAE-cellulose employing a CaCl₂ instead of Tris-HCl gradient. Both forms appear homogeneous on regular and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. In addition, both forms have a sp. act. of ca 700 units per A unit at 280 nm, similar to the potency of the pancreatic enzyme. DNase C and D, which are present in relatively small quantities in malt, were not characterized. The MWs of DNases A and B, as estimated by the SDS gel electrophoresis techniques, are near 32 000, slightly larger than that of the pancreatic enzyme. In the presence of either Mn²⁺ or Mg²⁺, the pH-activity profile of the barley enzyme is similar to that obtained with the pancreatic enzyme. Like the pancreatic enzyme, barley DNase is protected by Ca²⁺ from inactivation. The amino acid compositions of the A and B forms are about the same; a comparison of the malt and pancreatic enzymes shows many similarities but major differences in the amounts of glutamic acid, proline and glycine. The hydrolysis products of DNA by malt DNase are indistinguishable from those obtained with pancreatic DNase. Further hydrolysis of these products by snake venom phosphodiesterase shows malt DNase to be a 5′-phosphate producer. Deoxythymidine 3′,5′-di-p-nitrophenyl phosphate, one of the synthetic substrates of pancreatic DNase, is also hydrolysed by malt DNase.