title: Isolation and characterization of a ribonuclease from human leukemic blood cells specific for ribonucleic acid of ribonucleic acid-deoxyribonucleic acid hybrid molecules.
abstract: A ribonuclease that specifically hydrolyzes RNA in RNA. DNA hybrids has been purified more than 100-fold from human acute leukemic white blood cells. The molecular weight of this enzyme has been estimated as 80,000 by glycerol gradient centrifugation. It requires Mg-2plus for activity and is inhibited by N-ethylmaleimide. The optimum activity is observed at pH 8 (37 DEGREES). It is a heat-labile protein, t 1/2 at 50 degrees being 2 min. Among the substrates examined, (A)n X (dT)m, (I)n X (DC)m, and PHIX-174 DNA X RNA were hydrolyzed efficiently. (U)n X (dA)m showed a slight substrate activity, while (c) n X (dG) m and (G)n X (dC)m were not significantly hydrolyzed. The enzyme is an endonuclease and does not require RNA ends in the substrate molecule. It is capable of converting more than 95% of the RNA portions in hybrid substrates into acid-soluble products which are mono- and oligonucleotides terminated in 3'-OH and 5'-phosphate.
mesh_terms: D002499:Centrifugation, Density Gradient; D002852:Chromatography, Ion Exchange; D004254:DNA Nucleotidyltransferases / Q000097:blood; D004279:DNA, Viral; D005033:Ethylmaleimide / Q000494:pharmacology; D006358:Hot Temperature; D006801:Humans; D006863:Hydrogen-Ion Concentration; D015470:Leukemia, Myeloid, Acute / Q000201:enzymology*; D007962:Leukocytes / Q000201:enzymology*; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D009693:Nucleic Acid Hybridization; D012367:RNA, Viral; D012260:Ribonucleases / Q000097:blood* / Q000302:isolation & purification
chemical_list: D004279:DNA, Viral; D012367:RNA, Viral; D004254:DNA Nucleotidyltransferases; D012260:Ribonucleases; D008274:Magnesium; D005033:Ethylmaleimide