title: Inhibition and substrate competition kinetics in analysis of porcine thyroid alkaline ribonuclease's specificity toward synthetic RNA's and tRNA.
abstract: Inhibition and substrate competition kinetics demonstrated that tRNA is a highly preferred substrate of thyroid alkaline RNase. The pyrimidine-specific RNase cleaved poly(C) 2.8 x 10(5) faster than poly(U). kcat:K(M) ratios for tRNA and poly(C) based on molecular weights failed to predict preference when both were present. Competition experiments between poly(C) and tRNA revealed tRNA was a tight-binding competing substrate and the cytidylate residues in the 3'-CCA terminus to tRNA were preferred about 280:1 over those in poly(C). Poly(U) was competitive with tRNA. When poly(C) was the substrate, inhibition type by poly(G) depended on poly(G) concentration. Neither tRNA lacking its 3' terminal cytidylyl(3'-5')adenosine and terminating in a 2':3' cCMP residue, tRNA lacking its 3' terminal 5'AMP residue, guanosine, nor guanylyl(3'-5')guanylyl(3'-5')guanosine were inhibitors. Product inhibition by adenosine and 2':3' cCMP showed the kinetic mechanism for cleavage of tRNA was ordered uni bi.
authors.affiliation: Department of Biological Sciences, State University of New York at Binghamton 13902-6000, USA.
authors.forename: B E
authors.initials: BE
authors.lastname: Crute
authors.forename: J A
authors.initials: JA
authors.lastname: Markstein
authors.forename: F J
authors.initials: FJ
authors.lastname: Kull
mesh_terms: D000818:Animals; D007700:Kinetics; D008099:Liver / Q000737:chemistry; D009994:Osmolar Concentration; D011066:Poly C / Q000378:metabolism; D011072:Poly U / Q000378:metabolism; D012313:RNA / Q000138:chemical synthesis / Q000378:metabolism*; D012343:RNA, Transfer / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D012260:Ribonucleases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013379:Substrate Specificity; D013552:Swine; D013961:Thyroid Gland / Q000201:enzymology*
chemical_list: D011072:Poly U; D011066:Poly C; D012313:RNA; D012343:RNA, Transfer; D012260:Ribonucleases