Résumé
Astragalus membranaceus pathogenesis-related protein 10 (AmPR-10) is largely expressed in case of environmental pressure and pathogen invasion. This study aims to explore the biochemical functions of AmPR-10. The dried root of Astragalus membranaceus was mechanically homogenized and extracted by Tris-HCl buffer to obtain its crude extract, which was then purified by anion exchange chromatography and gel filtration chromatography to obtain electrophoretically pure AmPR-10. The nuclease activity of AmPR-10 was tested with different RNAs by detecting the absorption value at 260 nm. The results demonstrated potent nuclease activity toward yeast tRNA, yeast RNA, Poly (A) and Poly (C). The optimum reaction temperature was 50 °C and pH was 7-8. EDTA showed no effect on its activity, while Mg²⁺ exhibited potent activation effect on the activity, and Co²⁺, Ca²⁺ and Zn²⁺ manifested moderately inhibition of the activity. Since AmPR-10 had no sequence homology with other known nucleases, AmPR-10 was probably a novel nuclease. The inhibition kinetic data against papain was analyzed by Lineweaver-Burk plots, and the results showed that the inhibition of papain followed noncompetitive-type kinetics. AmPR-10 played an important role in Astragalus membranaceus defense mechanism against environmental pressure and pathogen invasion, which may be achieved by inhibiting cycteine enzymes activity.
Résumé
Con el objetivo de aislar y caracterizar parcialmente las enzimas ribonucleasas (RNasas) contenidas en el látex de Calotropis procera y Pedilanthus tithymaloides, se colectaron muestras de plantas adultas. Las proteínas solubles fueron extraídas con acetato de sodio y centrifugación a 16.000 x g durante 15 min y fraccionadas por cromatografía de intercambio iónico. Se estimó la masa molecular a través de ecuaciones de regresión lineal. Se realizaron pruebas de glicosilación. En ambas especies, las proteínas con actividad RNasa presentaron una masa molecular entre 28 y 30 kDa. No existe evidencia de proteínas glicosiladas en el látex de C. procera. En P. tithymaloides la RNasa es una proteína glicosilada.
In order to isolate and characterize partially ribonucleases (RNases) enzymes contained in the latex from Calotropis procera and Pedilanthus tithymaloides, samples were collected from mature plants. Soluble proteins were extracted with sodium acetate and centrifugation at 16,000 xg for 15 min and fractionated by ion exchange chromatography. Molecular mass was estimated by linear regression equations. Glycosylation tests were conducted. In both species, proteins with RNase activity showed a molecular mass between 28 and 30 kDa. No evidence of glycosylated proteins in latex from C. procera. In P. tithymaloides, RNase may be a glycosylated protein.