RESUMO
Arginyl- and lysyl-tRNA synthetases copurify throughout a six-step chromatographic procedure resulting in a purification of 605- and 559-fold, respectively. The purified enzymes were estimated to be 98% pure with a stoichiometry of 1:1 from acrylamide gel electrophoresis under denaturing conditions. On the basis of a native molecular weight of 285000 calculated from s20,w, Rs, and V and subunit molecular weights of 73000 and 65000 obtained by sodium dodecyl sulfate gel electrophoresis, the synthetases appear to exist as a tetramer. The tetrameric structure was also supported by cross-linking studies. These results are consistent with an alpha 2 beta 2 structure, but an alpha beta structure has not been ruled out.
Assuntos
Aminoacil-tRNA Sintetases/isolamento & purificação , Arginina-tRNA Ligase/isolamento & purificação , Fígado/enzimologia , Lisina-tRNA Ligase/isolamento & purificação , Animais , Cromatografia em Gel , Eletroforese em Gel de Poliacrilamida , Feminino , Focalização Isoelétrica , Substâncias Macromoleculares , Peso Molecular , RatosRESUMO
BACKGROUND: The benefit of catheter-based reperfusion for acute myocardial infarction (MI) is limited by a 5% to 15% incidence of in-hospital major ischemic events, usually caused by infarct artery reocclusion, and a 20% to 40% need for repeat percutaneous or surgical revascularization. Platelets play a key role in the process of early infarct artery reocclusion, but inhibition of aggregation via the glycoprotein IIb/IIIa receptor has not been prospectively evaluated in the setting of acute MI. METHODS AND RESULTS: Patients with acute MI of <12 hours' duration were randomized, on a double-blind basis, to placebo or abciximab if they were deemed candidates for primary PTCA. The primary efficacy end point was death, reinfarction, or any (urgent or elective) target vessel revascularization (TVR) at 6 months by intention-to-treat (ITT) analysis. Other key prespecified end points were early (7 and 30 days) death, reinfarction, or urgent TVR. The baseline clinical and angiographic variables of the 483 (242 placebo and 241 abciximab) patients were balanced. There was no difference in the incidence of the primary 6-month end point (ITT analysis) in the 2 groups (28.1% and 28.2%, P=0.97, of the placebo and abciximab patients, respectively). However, abciximab significantly reduced the incidence of death, reinfarction, or urgent TVR at all time points assessed (9.9% versus 3.3%, P=0.003, at 7 days; 11.2% versus 5.8%, P=0.03, at 30 days; and 17.8% versus 11.6%, P=0.05, at 6 months). Analysis by actual treatment with PTCA and study drug demonstrated a considerable effect of abciximab with respect to death or reinfarction: 4.7% versus 1.4%, P=0.047, at 7 days; 5.8% versus 3.2%, P=0.20, at 30 days; and 12.0% versus 6.9%, P=0.07, at 6 months. The need for unplanned, "bail-out" stenting was reduced by 42% in the abciximab group (20.4% versus 11.9%, P=0.008). Major bleeding occurred significantly more frequently in the abciximab group (16.6% versus 9.5%, P=0.02), mostly at the arterial access site. There was no intracranial hemorrhage in either group. CONCLUSIONS: Aggressive platelet inhibition with abciximab during primary PTCA for acute MI yielded a substantial reduction in the acute (30-day) phase for death, reinfarction, and urgent target vessel revascularization. However, the bleeding rates were excessive, and the 6-month primary end point, which included elective revascularization, was not favorably affected.