ABSTRACT
The hydrolysis of a 5' cap analogue, diadenosinyl-5',5'-triphosphate (ApppA), and two dinucleoside monophosphates: adenylyl(3',5')adenosine (ApA) and uridylyl(3',5')uridine (UpU) promoted by an imidazolate-bridged heterobinuclear copper(II)-zinc(II) complex, Cu(II)-diethylenetriamino-micro-imidazolato-Zn(II)- tris(aminoethyl)amine trisperchlorate (denoted as Cu,Zn-complex in the followings) has been investigated. Kinetic measurements were performed in order to explore the effects of pH, the total concentration of the Cu,Zn-complex and temperature on the cleavage rate. The catalytic activity of the Cu,Zn-complex was quantified by pseudo-first-order rate constants obtained in the excess of the cleaving agent. The results show that the Cu,Zn-complex and its deprotonated forms have phosphoesterase activity and with ApppA the metal complex promoted cleavage takes place selectively within the triphosphate bridge.
Subject(s)
Copper/chemistry , Dinucleoside Phosphates/chemistry , RNA Caps , RNA, Messenger/chemistry , Zinc/chemistry , HydrolysisABSTRACT
This review discusses the effects the secondary structure of an RNA molecule has on the inherent reactivity of its phosphodiester bonds, and on the catalytic activity of metal ion-based cleaving agents. The basic principles of the intramolecular transesterification of RNA phosphodiester bonds, particularly cleavage, are first briefly described. Studies of the structural effects on the cleavage, in the absence and in the presence of metal ion catalysts, are then reviewed, and the sources of the reactivity differences observed in different structures are discussed.
Subject(s)
Nucleic Acid Conformation , RNA/chemistry , RNA/metabolism , Base Sequence , Catalysis , Chemical Phenomena , Chemistry, Physical , Esterification , Hydrogen-Ion Concentration , Metals/chemistry , RNA, Catalytic/chemistry , RNA, Catalytic/metabolism , RNA, Double-Stranded/chemistry , RNA, Double-Stranded/metabolism , RNA, Transfer/chemistry , RNA, Transfer/metabolismABSTRACT
Uridylyl-(3',5')-8-carboxymethylaminoadenosine has been synthesised, and its transesterification to uridine 2',3'-cyclic phosphate in the presence and absence of Zn2+ ion has been studied. The results show that a carboxylate function in the vicinity of the phosphodiester bond accelerates the metal ion promoted cleavage but not the metal ion independent reaction. Under acidic conditions, the predominant reaction is the cleavage of the side chain, giving the 8-amino derivative.
Subject(s)
Dinucleoside Phosphates/chemistry , Hydroxides/chemistry , Models, Chemical , Onium Compounds/chemistry , Zinc/chemistry , Catalysis , Esters , Hydrolysis , Kinetics , Magnetic Resonance Spectroscopy , Spectrometry, Mass, Fast Atom BombardmentABSTRACT
PURPOSE: The aim of this prospective study was to determine the incidence of enlarged supraclavicular lymph nodes by US and the diagnostic yield of US-guided aspiration cytology in the diagnosis of sarcoidosis. METHODS: During a 54-month period, all consecutive patients with a clinical suspicion of sarcoidosis underwent supraclavicular US at the Kiljava Hospital, Finland. All patients with enlarged supraclavicular lymph nodes underwent US-guided fine-needle aspiration biopsy (FNAB) of the lymph node. RESULTS: Of a total of 250 patients, 27 (10.8%) had enlarged supraclavicular lymph nodes at US. All these were non-palpable at clinical examination. The cytological specimen was quantitatively sufficient in 25 of the 27 cases (93%). In 22 (88%) of these, the cytological diagnosis was granulomatous inflammation suggestive of sarcoidosis. Three aspirates yielded reactive hyperplasia and 2 specimens were insufficient. No complications occurred. The patients were followed for 2-42 months (mean 19 months), and the diagnosis of sarcoidosis was confirmed clinically in all cases. CONCLUSION: Supraclavicular US detects non-palpable enlarged lymph nodes in 1/10 of the patients with suspected sarcoidosis. In this subgroup of patients, US combined with aspiration cytology may give cytological evidence of granulomatous disease similar to sarcoidosis and more invasive diagnostic methods can be avoided.