Purification and subunit structure studies of human placental threonyl-tRNA synthetase

Human threonyl-tRNA synthetase has been purified from full-term placenta over 5000-fold with a 13% overall yield by a combination of affinity chromatographic methods and conventional procedures. The product was apparently homogeneous by the criterion of sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified enzyme catalyzed the esterification of ? 3500 nmol L-threonine to tRNA per min per mg of protein at 37°, corresponding to a molecular activity of ? 700/min. The apparent molecular weight of the native enzyme ranged from 210 000 to 220 000 by gel-filtration on Sephadex G-200, and was either ? 110 000 or 228 000 by sucrose gradient centrifugation for different preparations. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated a single band of molecular weight 85 000 or 115 000 for different preparations. These results suggest that human placental threonyl-tRNA synthetase has a subunit structure of the type α₂ with a subunit molecular weight of about 100 000. However, some other molecular forms with lower specific activity were also found to exist under certain conditions.     

双稠吡咯啶生物碱的研究 Ⅰ.森林千里光的生物碱

从浙江天目山采集的森林千里光(Senecio nemorensis)中分得二个双稠吡咯啶类型的生物碱,其中之一熔点为55—57℃,分子式为C₁₃H₂₁O₃N。另一熔点为42—43℃,分子式为C₁₈H₂₇O₅N。由其理化常数及酒石酸盐、苦味酸盐、水解产物等结果,与文献上记载的大叶千里光中所得的macrophylline及从瓶草千里光中所得的sarracine比较,证明前者与macrophylline相同,而后者与sarracine相同。