Graeff Richard M, Lee Hon Cheung
Department of Physiology, The University of Hong Kong, Hong Kong, China.
Methods Mol Biol. 2013;1016:39-56. doi: 10.1007/978-1-62703-441-8_4.
Cyclic ADP-ribose (cADPR) is a novel second messenger that releases calcium from intracellular stores. Although first shown to release calcium in the sea urchin egg, cADPR has been shown since to be active in a variety of cells and tissues, from plant to human. cADPR stimulates calcium release via ryanodine receptors although the mechanism is still not completely understood. cADPR is produced enzymatically from NAD by ADP-ribosyl cyclases; several of these proteins have been identified including one isolated from Aplysia californica, two types found in mammals (CD38 and CD157), and three forms in sea urchin. A cyclase activity has been measured in extracts from Arabidopsis thaliana although the protein is still unidentified. Nicotinic acid adenine dinucleotide phosphate (NAADP) is another novel messenger that releases calcium from internal stores and is produced by these same enzymes by an exchange reaction. NAADP targets lysosomal stores whereas cADPR releases calcium from the endoplasmic reticulum. Due to their importance in cell signaling, cADPR and NAADP have been the focus of numerous investigations over the last 25 years. This chapter describes several assay methods for the measurements of cADPR and NAADP concentration and cyclase activity in extracts from cells.
环磷酸腺苷核糖（cADPR）是一种新型的第二信使，可从细胞内储存库释放钙。尽管最初发现它能在海胆卵中释放钙，但此后已证明cADPR在从植物到人类的各种细胞和组织中都具有活性。cADPR通过兰尼碱受体刺激钙释放，不过其机制仍未完全明确。cADPR由ADP核糖基环化酶从NAD酶促产生；已鉴定出几种此类蛋白质，包括一种从加州海兔分离出的蛋白质、在哺乳动物中发现的两种类型（CD38和CD157）以及海胆中的三种形式。尽管尚未鉴定出拟南芥提取物中的蛋白质，但已检测到其环化酶活性。烟酰胺腺嘌呤二核苷酸磷酸（NAADP）是另一种新型信使，可从内部储存库释放钙，并且由这些相同的酶通过交换反应产生。NAADP作用于溶酶体储存库，而cADPR则从内质网释放钙。由于它们在细胞信号传导中的重要性，在过去25年中，cADPR和NAADP一直是众多研究的焦点。本章介绍了几种用于测量细胞提取物中cADPR和NAADP浓度以及环化酶活性的测定方法。
