RESUMEN
Caffeine is a major component of xanthine alkaloids and commonly consumed in many popular beverages. Due to its occasional side effects, reduction of caffeine in a natural way is of great importance and economic significance. Recent studies reveal that caffeine can be converted into non-stimulatory theacrine in the rare tea plant Camellia assamica var. kucha (Kucha), which involves oxidation at the C8 and methylation at the N9 positions of caffeine. However, the underlying molecular mechanism remains unclear. Here, we identify the theacrine synthase CkTcS from Kucha, which possesses novel N9-methyltransferase activity using 1,3,7-trimethyluric acid but not caffeine as a substrate, confirming that C8 oxidation takes place prior to N9-methylation. The crystal structure of the CkTcS complex reveals the key residues that are required for the N9-methylation, providing insights into how caffeine N-methyltransferases in tea plants have evolved to catalyze regioselective N-methylation through fine tuning of their active sites. These results may guide the future development of decaffeinated drinks.
Asunto(s)
Cafeína/metabolismo , Metiltransferasas/metabolismo , Té/enzimología , Ácido Úrico/análogos & derivados , Sitios de Unión , Vías Biosintéticas , Cafeína/química , Clonación Molecular , Cristalografía por Rayos X , Evolución Molecular , Regulación de la Expresión Génica de las Plantas , Metilación , Metiltransferasas/química , Hojas de la Planta/química , Proteínas Recombinantes/metabolismo , Té/genética , Transcripción Genética , Ácido Úrico/química , Ácido Úrico/metabolismoRESUMEN
AIM: To investigate the effects of genistein on bone mineralization in ovariectomized rats. METHODS: Forty-seven Wistar rats were randomly allocated into six groups: sham-operated (sham), ovariectomized (ovx), ovariectomized supplied with diethyl stilbestrol (E, 20 microg x kg bw(-1) x d(-1)) or genistein (25, 50, 100 mg x kg bw(-1) x d(-1)). After the rats had been fed for three months, analysis of the bone mineral density, parameters related to mineralization, bone content of Ca, P, Mg, Mn and Zn and serum concentration of parathyroid calcitonin and estrogen was performed. RESULTS: Bone mineral density, bone Ca, P, Zn and Mg content and serum estrogen concentration in ovariectomized rats were significantly decreased, but mean osteoid width increased, mineralization lag time and osteoid maturation period prolonged compared with sham animals. After three months supplementation to ovariectomized rats, bone Ca, P and Mg content increased, mean osteoid width decreased, mineralization lag time and osteoid maturation period shortened compared with ovariectomized animals. CONCLUSION: Genistein promotes bone mineralization by increasing bone Ca, P, Mg and adjusting serum calcitonin to prevent osteoporosis.