title: Preparation of the bifunctional enzyme ribonuclease-deoxyribonuclease by cross-linkage.
abstract: Protease-free bovine pancreatic deoxyribonuclease (DNase) (1.6 X 10(-4) mmol) was thiolated on the NH2 groups with N-acetyl-DL-homocysteine thiolactone (2.4 X 10(-2) mmol) at pH 10.5 with imidazole (2.4 X 10(-2) mmol) as the catalyst in the presence of 4,4'-dithiodipyridine (4.2 X 10(-2) mmol). The product obtained after 16 h at 4 degrees C, 2-acetamido-4-(4'-dithiopyridyl)butyryl-DNase, isolated by gel filtration, contained an average of 0.87 +/- 0.13 mol of mixed disulfide per mol of DNase. Ribonuclease (RNase) was thiolated in a similar manner, but under N2 in the absence of 4,4'-dithiodipyridine. The protein N-acetylhomocysteinyl-RNase contained on the average 0.94 +/- 0.11 mol of sulfhydryl groups per mol of RNase. The coupling of RNase ot DNase was accomplished by thiol-disulfide interchange at pH 6.2 and 25 degrees C for 90 min. The hybrid enzyme (yield 25--33%, based upon the DNase derivative used) was freed from unreacted DNase, RNase, and homodimers by gel filtration, affinity chromatography, and salting-out chromatography. The purified enzyme contained one molecule each of DNase and RNase and hydrolyzed thymus deoxyribonucleic acid (DNA) and yeast or transfer ribonucleic acid (RNA) with 75 and 40% of the efficiencies, respectively, of the parent enzymes. The RNA strand of the hybrid substrate, phage f1 DNA-[3H]RNA, prepared from phage DNA with RNA polymerase, was hydrolyzed rapidly by the hybrid enzyme but was not hydrolyzed by RNase alone. A conjugate of the two enzymes offers the possibility in vivo of delivering two enzymes that differ in size, charge, and biological function to the same site at the same time.
mesh_terms: D000818:Animals; D002417:Cattle; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D003432:Cross-Linking Reagents; D003851:Deoxyribonucleases / Q000302:isolation & purification / Q000378:metabolism*; D004220:Disulfides; D007700:Kinetics; D010179:Pancreas / Q000201:enzymology; D012260:Ribonucleases / Q000302:isolation & purification / Q000378:metabolism*; D013438:Sulfhydryl Compounds
chemical_list: D003432:Cross-Linking Reagents; D004220:Disulfides; D013438:Sulfhydryl Compounds; D003851:Deoxyribonucleases; D012260:Ribonucleases