title: Inhibition of ribonucleases by ribonucleotides and transition state analogs in cell-free extracts from Ehrlich ascites tumor cells.
abstract: We investigated the ribonucleolytic breakdown of poly(U), poly(A), RNA trascribed from calf thymus DNA with E. coli RNA polymerase, ribosomal RNA, tRNA and mengovirus RNA by an enzyme fraction obrained from a postribosomal supernatant of Ehrlich ascites tumor cells. The single-stranded homopolyribonucleotides are preferentially degraded by the enzyme fraction with the production of ribonucleoside 5'-monophosphates. The RNase activity is completely dependent on the presence of Mg2+ ions and is highest at Mg2+ and K+ concentrations optimal for cell-free protein synthesis. Ribonucleoside 5'-monophosphates, ribonucleoside 2'(3')-monophosphates, ribonucleoside 2'(3'),5'-bisphosphates and transition state analogs consisting of vanadyl sulfate and either ribonucleosides or ribonucleoside 5'-monophosphates in a molar ratio 1:1 inhibit the ribonucleolytic activity of the enzyme fraction. The ribonucleoside 2'(3'),5'-bisphosphates and the transition state analogs are the most effective inhibitors. However, only in the presence of ribonucleoside 2'(3'),5'-bisphosphates a concomitant stimulation by 50 to 60% of poly(U)-directed polyphenylalanine synthesis is observed; all the other RNase inhibitors tested also inhibit polypeptide synthesis. The results of preliminary experiments show that poly(U) and ribonucleoside 2'(3'),5'-bisphosphates are well suited as ligands for affinity chromatography of ribonucleases from Ehrlich ascites tumor cells.
mesh_terms: D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000201:enzymology*; D002417:Cattle; D002457:Cell Extracts; D002474:Cell-Free System; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D012329:RNA, Bacterial / Q000378:metabolism; D012335:RNA, Ribosomal / Q000378:metabolism; D012260:Ribonucleases / Q000037:antagonists & inhibitors*; D012265:Ribonucleotides / Q000494:pharmacology*; D013347:Subcellular Fractions
chemical_list: D002457:Cell Extracts; D012329:RNA, Bacterial; D012335:RNA, Ribosomal; D012265:Ribonucleotides; D012321:DNA-Directed RNA Polymerases; D012260:Ribonucleases