CD38-综述.doc

CD38是一个定位于膜上的糖蛋白，催化环腺苷二磷酸核糖（cADPR, cyclic ADP-ribose）的合成和降解。cADPR是核苷酸的代谢产物，通过作用于ryanodine受体（RyRs）参与细胞内钙库的钙动员。许多研究发现CD38/cADPR介导的Ca2+信号传递和通过RyRs通道的Ca2+释放在Ca2+内平衡的调控中发挥了重要的作用。CD38/cADPR/ RyRs介导的Ca2+信号传递也参与了许多病理和生理过程。本文就CD38基因的结构、表达、调控及在心血管系统的功能做一综述。结构：cd38基因包括了8个外显子，5UTR无TATA盒或CAAT盒（Nata K, Takamura T, Karasawa T, Kumagai T, Hashioka W, Tohgo A, Yonekura H, Takasawa S, Nakamura S, and Okamoto H. Human gene encoding CD38 (ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase): organization, nucleotide sequence and alternative splicing. Gene 186: 285292, 1997.）。一段高GC含量区可能是cd38的启动子区，调节CD38的表达。CD38 是一个45kDa的单链跨膜糖蛋白，整体结构分为N末端短的胞质尾，单次跨膜域和C端长的胞外区（图 1）。其开放阅读框含有300个氨基酸残基，5UTR比较短小，69bp；3UTR含有260bp，不包括PolyA尾。其编码的多肽链分子量为34，288道尔顿。天然的CD38抗原的分子量为46，000道尔顿。预测的氨基酸序列没有N-末端的引导肽序列，但在从翻译起始位点起21个氨基酸残基处含有一段长23个氨基酸残基的内部疏水序列。CD38原始序列的亲水性图提示CD38分子仅跨膜一次，也就是说多肽链的长C-末端指向胞外，N-末端有19aa的短胞质尾。（pDavid G. Jackson, John I. Bell, Isolation of a cDNA encoding the human CD38(T10) molecule, a cell surface glycoprotein with an unusual discontinuous pattern of expression during lymphocyte differentiation. The Journal of Immunology, 1990 144(7) 2811-2815）人类、大鼠和小鼠CD38基因的cDNA已被克隆（Jackson, D.C., and Bell, J. I. (1990) Isolation of a eDNA encoding the human CD38 (T10) molecule, a cell surface glycoprotein with an unusual discontinuous pattern of expression during lymphocyte differentiation. J. Immunol. 144,2811-2817; Harada, N., Santos-Argumedo, L., Chang, R., Grimaldi, C. J., Lund, F. E.,Brannan, C. I., Copeland, N. G., Jenkins, N. A., Heath, A. W., Parkhouse,R. M., and Howard, M. (1993) Expression cloning of a eDNA encoding a novel murine B cell activation marker: homology to human CD38. J. immunol.151, 3111-3118; Koguma, T., Takasawa, S., Tohgo, A., Karasawa, T., Furuya, Y., Yonekura,H., and Okamoto, H. (1994) Cloning and characterization of eDNA encoding rat ADP-ribosyl cyclase/cyclic ADP ribose hydrolase from islets of Langerbans. Biochim. Biophys. Acta 1223, 160-162），三种来源的CD38蛋白的氨基酸序列表现出了高的同源性（表 1）。由于CD38的蛋白具有N端在胞内，C端在胞外这种结构上的特点，因此属于型膜蛋白。CD38 蛋白胞外部分近C-末端有4个潜在的N-连接糖基化位点，24个含有唾液酸的高甘露糖N-连接寡糖链，占其蛋白分子量的25%，还有一个可能的透明质酸结合基序在其胞外域。 运用体细胞遗传学方法将人CD38蛋白的编码基因定位在4号染色体（Katz, F., Povey, S., Parkar, M., Schneider, C., Sutherland, R., Stanley, K., Solomon, E., and Creaves M. (1983) Chromosome assignment of monoclonal antibody-defined determinant on human leukemic cells. Eur. J. Immunol.13, 1008-1013）。随后被进一步定位到4p15（Nakagawara, K., Mori. M., Takasawa, S., Nata, K., Takamura, I., Berlova, A., Tohgo, A., Karasawa, T., Yonekura, H., Takeuchi, T., and Okamoto, H. (1995) Assignment of CD38, the gene encoding human leukocyte antigen CD38 (ADP-ribosyl cyclase/cyclic ADP rihose hydrolase), to chromosome 4p15. Cyogene:. Cell. Genet. 69,38-39）。CD38在鼠类中的同源基因位于5号染色体。与HOX7（4p16.3-P16.1），KIT(4p12)等基因成簇分布人类的4号染色体和小鼠的5号染色体上。 图 1 CD38 结构示意图表1 CD38 Mol.massMembrane%Amino acidChromosomalMoleculekDaassociationsimilarityDistributionassignmentHuman CD3843.7TM100Hemopoietic,other4p15Murine CD3842TM70B,T,and NK cells, monocyte/macrophages5Rat CD 3834.4TM76Spleen, liver, heart, thymus ileum, colon, salivary glands, pancreatic islet cells?TM, transmembraneCD38除了锚钉在细胞膜上外（45kDa, mCD38），还以可溶性的形式存在（39kDa, sCD38），可能为细胞膜蛋白被剪切的结果。因此，在体外培养的T淋巴细胞异常激活及CD38+的肿瘤细胞系的培养液中可以检测到CD38。在正常的羊水中及多发性黑色素瘤患者的血清和腹水中也可检测到sCD38。（FunaroA, HorensteinAL, MalavasiF., Human CD38: a versatile leukocyte marker with emerging clinical prospectives. Fundamental Clin. Immunol. 1995, 3, 101-113）。体外实验中mCD38的脱落可被特异性的CD38抗体诱导，及N-p-ptosyl-L-lysine chloromethyl ketone(一种丝氨酸蛋白酶抑制剂)抑制。提示CD38可能为某种未知配体的受体，如同许多白细胞膜上的受体，与相应的配体或模拟配体的抗体相互作用后被酶切脱离细胞膜。（MehtaK, AggarwalBB, Recombinant organisms as source of cancer biotherapeutics. In Principles of Cancer Biotherapy. 1996）在维甲酸诱导下培养的人髓细胞性白血病细胞中又发现了mCD38高分子量形式，190kDa。该高分子量形式是在转谷氨酰胺酶催化下的转录后mCD38的交联。dUmarS, MalavasiF, MehtaK, Post-translational modification of CD38 protein into a high molecular weight form alters its catalytic properties. J. Biol. Chem. 1996, 271, 15922-27。表达：该分子的分布比最初认为的要广泛的多（表 2）。在多种类型的细胞中均有表达。CD38 in humansLymph node Lymphoblast germinal cells, plasma cells, and interfollicular cellsThymus Paracortical and mainly medullaiy thymocytesBrain Perikaryal anddendriiic cytoplasm of neuronsDigestive tract Lamina propria lymphocytesKidney Proximal tubuliProstate Cytoplasmic membrane and secretory vacuolesSkeletal and Sarcolemmin of myocites and cardiomyocitescardiac musclesCD38 in mouseLymphocytes Predominantly B Cells and cell lines; variable proportions of T cells (10-40% of PBMC) and thymocytes (8-10%, mainly ICR, CD4, CD8)Myeloid cells Variable proportions: MAC-i macrophages from peritoneum are CD38; unstimulated BM macrophages are CD38; BM-denved cell lines in GM-CSF are CD38CD38的表达随着年龄的变化而变化，新生婴儿中90%的循环淋巴细胞为阳性；6-10岁时只有50-60%的淋巴细胞呈阳性表达。成年人中，CD38在大多数自然杀伤细胞、T细胞、B细胞，单核细胞/巨噬细胞（MalavasiF, Caligaris-CappioF, DellabonaP, et.al. Characterization of a murine monoclonal antibody specific for human early lumphohemopoietic cells. Human Immunol. 1984, 9, 9-20。血小板dRamaschiG, TortiM, TolnaiF, et.al., Expression of cyclic ADP-ribos-synthesizing CD38 molecule on human platelet membranes. Blood, 1996, 87, 2308-2313和红细胞ZocchiE, FrancoL, GuidaL, et.al., Single protein immunologically identified as CD38 displays NAD+ glycohydrolase and cyclic ADP-ribose hydrolase activities at the outer surface of human erythrocytes. Biochem. Biophys. Res. Commun. 1993, 196, 1459-1465）上也有一定程度的表达。对糖的需求量很大的组织如胰腺、脑、脾和肝也有相对高的CD38的表达KogumaT, TakasawaS, TohgoA., et.al. Cloning and characterization of cDNA encoding rat ADP-ribosyl cyclase/cyclic ADP ribose hydrolase from islets of Langerhans. Biochim. Biophys. Acta 1994, 1223, 160-162。CD38在胰腺的胰岛细胞受葡萄糖诱导分泌胰岛素方面发挥了重要作用。在消化道固有膜的淋巴细胞中也可以检测到CD38（J.Fernandez Barbero and M. Boirivant, unpublished results）。肾曲小管，骨骼肌和心肌的肌膜也有CD38的表达，间接的证实了在某些特定的细胞系中观察到的可诱导钙离子释放的激动性抗体可激发CD38的表达的现象MalavasiF, FunaroA, AllesioM, et.al., CD38: a multilineage cell activation molecule with a split personality. Int. J. Clin. Lab. Res. 1992, 22, 73-80。CD38在神经元中的表达表现为核周及树突胞质中颗粒状染色，提示其与细胞内细胞器的联系。这些发现在神经系统疾病模型中得到肯定，CD38的免疫反应性同Alzheimer病的组织学标记神经纤维缠结相关MizuguchiM, OtsukaN, SatoM, et.al. Neuronal localization of CD38 antigen in the human brain. Brain Res. 1995, 697, 235-240。胰岛细胞（TakasawaS, NataK, YonekuraH, et.al., Cyclic ADP-ribose in insulin secretion from pancreatic beta cells. Science, 1993, 159, 370-373）、神经元（DeFloraA, GuidaL, FrancoL et.al., Ectocellular in vitro and in vivo metabolism of cADP-ribose in cerebellum. Biochem. J. 1996, 320, 665-671）和平滑肌细胞（dChiniEN, de ToledoFG, ThompsonMA, et al., Effect of estrogen upon cyclic ADP ribose metabolism: beta-estradiol stimulates ADP ribosyl cyclase in rat uterus. Pros. Natl. Acad. Sci. USA. 1997, 94,5872-5876; dDeshpandeDA, WalsethTF, PanettieriRA, et al., CD38cyclic ADP-ribose-mediated Ca2+ signaling contributes to aiway smooth muscle hyper-responsiveness. FASEB J. 2003, 17, 452-454; pDoganS, WhiteTA, DeshpandeDA, et al., Estrogen increase CD38 expression and leads to differential regulation of adenosine diphosphate (ADP)-ribosyl cyclase and cyclic ADP-ribose hydrolase activities in rat myometrium. Biol. Reprod. 2002, 66, 596-602）也有表达。小鼠CD38主要表达在B淋巴细胞。正常的或转化的B淋巴细胞均有表达LundF, SolvasonN, GrimaldiJC, et.al., Murine CD38: an immunoregulatory ectoenzyme. Immunol. Today, 1995, 16, 469-473。T淋巴细胞和髓样细胞也不同程度的表达膜表面CD38，但表达的量相对比不如人类的高。这种表达的偏差可以解释为鼠CD38属于CD38家族，但并不是人CD38抗原的完全一致的类似物。大鼠CD38的相关信息很有限，还不足以直接与人类和小鼠的CD38进行比对。大鼠CD38的mRNA在脾脏、肝脏、心脏、胸腺、甲状腺、肾上腺、空肠和胰岛有表达KogumaT, TakasawaS, TohgoA, et.al., Cloning and characterization of cDNA encoding rat ADP-ribosyl cyclase/cyclic ADP ribose hydrolase from islets of langerhans. Biochim. Biophys. Acta 1994, 1223, 160-162。调控：CD38的表达受到激素、维甲酸、细胞因子和维生素D3的调控（Ferrero E, Saccucci F, and Malavasi F. The making of a leukocyte receptor: origin, genes and regulation of human CD38 and related molecules. Chem Immunol 75: 119, 2000.；Genazzani AA and Galione A. A Ca2+ release mechanism gated by the novel pyridine nucleotide, NAADP. Trends Pharmacol Sci 18: 108110, 1997. Mehta K. Retinoid-mediated signaling in CD38 antigen expression. Chem Immunol 75: 2038, 2000.）。在CD38的启动子区有糖皮质激素反应元件和半个雌激素结合回文基序（Ferrero E, Saccucci F, and Malavasi F. The making of a leukocyte receptor: origin, genes and regulation of human CD38 and related molecules. Chem Immunol 75: 119, 2000.）。雌激素可增加CD38在子宫平滑肌中的表达，而孕激素可减弱由雌激素引起的CD38表达增强的效应。该现象可能与子宫平滑肌的收缩功能相关，雌激素引起的CD38表达增加，并伴随合成活性增强，分解活性不变，从而导致cADPR的合成增加，降解相对减少，促进钙离子从SR释放，增强子宫平滑肌的收缩，促进分娩。（pRegulation of CD38 expression and function by steroid hormones in myometrium. DoganS, DeshpandeDA, WhiteTA, Molecular and Cellular Endocrinology, 2006(246)101-106）。对于调节CD38酶催化功能的物质知之甚少。在海胆卵中，3，5-环一磷酸鸟苷能激活ADP核糖环化酶（Galione. A., White. A., Willmott. N,. Turner, M.Potter. B. V., and Watson.S. P. (1993) cGMP mobilizes intracellular Ca + in sea urehin eggs by stimulating cyclic ADP-ribose synthesis. Nature (London) 365,456-459）。虽然没有发现ADP核糖环化酶的cGMP依赖性磷酸化，但在CD38和海兔环化酶上都发现了磷酸化的保守序列。ATP也可特异性的抑制CD38的水解活性，环化酶活性不受影响，导致了cADPR的堆积（Takasawa, S., Tohgo, A., Noguchi, N., Koguma, T., Nata, K., Sugimoto, T., Yonekura, H., and Okamoto, H. (1993) Synthesis and hydrolysis of cyclic ADP-ribose by human leukocyte antigen CD38 and inhibition of the hydrolysis by ATP. J. Biol. Chem. 268,26052-26054）。人CD38在NAD+和巯基乙醇存在的条件下会形成稳定的寡聚化，伴随着ADP核糖环化酶和NADase活性的下降（Zocchi, E., Franco, L., Guida, L., Calder, L, and De Flora, A. (1995) Self-aggregation of purified and membrane-bound erythrocyte CD38 induces extensive decrease of its ADP-ribosyl cyclase activity. FEBS Lett. 359,35-40）。自聚集现象可看成是下调cADPR依赖性事件的机制。如人类的髓细胞性白血病细胞株（HL-60），给予RA治疗可引起CD38的迅速聚集（Kontani, K., Nishina, H., Ohoka, Y., Takahashi, K., and Katada, T. (1993) NAD glycohydrolase specifically induced by retinoic acid in human leukemic HL-60 cells. J. Biol. Chem. 268, 16895-16898; Drach, J., Zhao, S., Malavasi, F., and Mehta, K. (1993) Rapid induction of CD38 on myeloid leukemia cells by retinoic acid. Biochem. Biophys. Res.Commun. 195,545-550; Drach, J., McQueen, T., Engel, H., Andreeff, M., Robertson, K. A., Collins,S. J., Malavasi, F., and Mehta, K. (1994) Retinoic acid-induced expression of CD38 antigen in myeloid cells is mediated through retinoic acid receptor-alpha.Cancer Res. 54, 1746-1752）。CD38合成后经历了翻译后的修饰形成高分子量形式（190kDa）。与最初的45 kDa的天然形式相比，这个形式的CD38环化酶活性增加了4倍，水解酶活性降低了3倍（Umar, S., Malavasi, F., and Mehta, K. (1996) Post-translational modification of CD38 protein into a high molecular weight form alters its catalytic properties. J. Biol. Chem. 271, 15922-15927）。CD38的这种修饰有可能是体内对这种双功能酶的催化活性调控的重要机制。膜CD38的表达受到了许多生理性或药物性物质的调节，如细胞因子、RA和凝集素。这些物质在不同的细胞系均可上调CD38的表达。RA诱导的CD38的表达备受关注的。总的来说，成熟的循环中的髓样细胞不表达CD38，也不会在RA的诱导下表达。但在骨髓中的未成熟的髓样细胞却有相对高的表达量，在RA的治疗下还可进一步增加（Drach, J., McQueen, T., Engel, H., Andreeff, M., Robertson, K. A., Collins,S. J., Malavasi, F., and Mehta, K. (1994) Retinoic acid-induced expression of CD38 antigen in myeloid cells is mediated through retinoic acid receptor-alpha.Cancer Res. 54, 1746-1752）。同样，转化的髓样白血病细胞如HL-60、KG-1和NB4检测到了mCD38,并在RA的治疗诱导下迅速上调。Femtomolar浓度的RA就可引起CD38在转录和翻译水平明显快速的增加（Drach, J., Zhao, S., Malavasi, F., and Mehta, K. (1993) Rapid induction of CD38 on myeloid leukemia cells by retinoic acid. Biochem. Biophys. Res.Commun. 195,545-550；Drach, J., McQueen, T., Engel, H., Andreeff, M., Robertson, K. A., Collins,S. J., Malavasi, F., and Mehta, K. (1994) Retinoic acid-induced expression of CD38 antigen in myeloid cells is mediated through retinoic acid receptor-alpha.Cancer Res. 54, 1746-1752；Malavasi, F., Funazo, A., Roggero, S., Horenstein, A., Calosso, L, and Mehta,K. (1994) Human CD38: a glycoprotein in search of a function. Immunol.Today 15,95-97）。维甲酸诱导的CD38的表达十分特异，其他的可以诱导HL-60分化的物质如二甲基亚砜（dimethylsulfoxide）不会影响CD38的表达。这些结果提示了CD38的表达与沿特定分化信号途径分化的细胞命运不相关。维甲酸诱导的CD38的表达受到RAR（RA receptor alpha）型核受体的调控（Drach, J., McQueen, T., Engel, H., Andreeff, M., Robertson, K. A., Collins,S. J., Malavasi, F., and Mehta, K. (1994) Retinoic acid-induced expression of CD38 antigen in myeloid cells is mediated through retinoic acid receptor-alpha.Cancer Res. 54, 1746-1752； Mehta, K., McQueen, T., Neamati, N., Collins, N., and Andreeff, M. (1996) Activation of retinoid receptors RAR and RXR induces differentiation and apoptosis, respectively, in HL-60 cells. Cell Growth Differ. 7, 179-186），在使用RA单一口服剂量的白血病患者体内也观察到了这个现象（Drach, J., Zhao, S., Malavasi, F., and Mehta, K. (1993) Rapid induction of CD38 on myeloid leukemia cells by retinoic acid. Biochem. Biophys. Res.Commun. 195,545-550；）。在肾表皮细胞维甲酸是cADPR特异性的潜在的诱导者（Beers, K. W., Chini, E. N., and Dousa, T. P. (1995) All-trans-retinoic acid stimulates synthesis of cyclic ADP-ribose in renal LLC-PK1 cells.J.Clin.Invest. 95,2385-2390）。RA的一些生物学效应可能是通过CD38合成的cADPR发挥的。在另一方面，CD38的下降调节知之甚少。目前还没有证据证实有某种物质可以直接激发CD38的下调。最近发现在特定的情况下细胞表面表达的CD38会减少，如细胞培养密度过高或细胞激活时，细胞表面的CD38下调。CD38的可溶形式在体内特定的体液中也可检测到（Funaro, A., Horenstein, A. L., and Malavasi, F. (1995) Human CD38: a versatile leukocyte marker with emerging clinical prospectives. Fundamental Clin. Immunol. 3,101-113）。CD38可溶性形式的存在提示其有可能是某种未知配体的受体。有研究发现T细胞对内皮细胞的黏附能特异性的被抗CD38单克隆抗体抑制。CD38介导的黏附作用只在动态的情况下发挥功能，整联蛋白（integrin）的功能被最小化了，CD38的配体表现的像一个选择素（Dianzani, U., Funaro, A., DiFranco, D., Garbanno, G., Bragardo, M., Redoglia, V., Buonfiglio, D., DeMonte, L B., Piled, A., and Malavasi, F. (1994) Interaction between endothelium and CD4/CD45RA lymphocytes. Role of the human CD38 molecule.J. Immunol. 153,952-959）。这些结果提示了人内皮细胞表面可能有识别CD38阳性细胞的表面受体。CD38也可能是黏附分子的受体，在骨髓间质微环境中介导相互作用。 添加了CD38单克隆抗体的B细胞祖细胞间质支持的骨髓培养可见7天后细胞复原减少。也会抑制间质培养或间质来源的无细胞因子培养的未成熟的淋巴细胞系的生长。这些效应并非来自单克隆抗体介导的CD38酶活性的改变，说明了CD38与未知配体的结合对调节B淋巴细胞生成有新的机制（Kumagai, M., Coustan-Smith, E., Murry, D. J., Silvennoinen, 0., Murti, C. P., Evans, W. E., Malavasi, F., and Campana, D. (1995) Ligation of CD38 suppresses human B lymphopoiesis. J. Exp. Med. 181, 1101-1110）。最近鉴定出的一系列人类内皮细胞单克隆抗体中有一种是CD38的受体（Deaglio, S., Dianzani, U., Horestein, A. L, Fernandez, J.E., Van Kooten, C.,Bragardo, M., Garbanino, C., Funaro, A., DiVirgilio, F., Banchereau, J., and Malavasi, F. (1996) Human CD38 ligand. A 120-kDa protein predominantly expressed by endothelial cells.). Immunol. 156, 727-734）。好几个抗体都能与内皮细胞相互作用，只有Moon-1可以封闭CD38介导的CD38+细胞黏附到脐带内皮细胞作用。通过免疫组化的方法分析Moon-1在正常人体组织的分布，发现其具有独特的表达模式，在静止和活化的内皮细胞，大多数单核细胞，血小板，自然杀伤细胞，少数的T、B淋巴细胞和髓样细胞中高水平表达。从免疫沉淀和westernblot的结果推测CD38在非还原状态下的分子量约120kDa。抗体诱导的调变实验（modulation experiment）突出了同时表达这两种分子的细胞系的细胞表面的Moon-1和人CD38分子间的横向联系，似乎这两种分子具有同一套表面表达的调控系统。Western blot的结果也证实了可溶性的人CD38-鼠CD38嵌合体分子直接与免疫沉淀的Moon-1结合，为Moon-1是人CD38的配体提供了进一步的证明（Deaglio, S., Dianzani, U., Horestein, A. L, Fernandez, J.E., Van Kooten, C.,Bragardo, M., Garbanino, C., Funaro, A., DiVirgilio, F., Banchereau, J., and Malavasi, F. (1996) Human CD38 ligand. A 120-kDa protein predominantly expressed by endothelial cells.)。功能：酶功能：人和鼠的CD38与ADP核糖环化酶在结构上高度同源（States, D. J., Walseth, T. F., and Lee, H. C. (1992) Similarities in amino acid sequences of Aplysia ADP-ribosyl cyclase and human lymphocyte antigen CD38. Trends Biochem. Sci. 17,495）。ADP核糖环化酶催化NAD+生成cADPR，cADPR在细胞内作为第二信使，参与Ca2+的动员（Lee, H. C., Galione, A., and Walseth, T. F. (1994) Cyclic ADP-ribose: metabolism and calcium mobilizing function. In Vitamins and Hormones(Litwack, C., ed) pp. 199-258, Academic Press, Orlando, Florida）。CD38 和ADP核糖环化酶的共同特点在于它们拥有10个保守的半胱氨酸残基（States, D. J., Walseth, T. F., and Lee, H. C. (1992) Similarities in amino acid sequences of Aplysia ADP-ribosyl cyclase and human lymphocyte antigen CD38. Trends Biochem. Sci. 17,495），提示这两个蛋白可能具有相同的二级结构和三级结构，由此推测CD38可能具有ADP核糖环化酶的功能。在对经过纯化的CD38蛋白的胞外结构域形成的融合蛋白进行测试后，证实了其具有将NAD+环化为环腺苷二磷酸核糖（cADPR）的能力，及水解cADPR为ADPR的能力（Howard, M., Grimaldi, J. C., Bazan, F., Lund, F. E., Santos-Argumedo, L., Parkhouse, R. M., Walseth, T. F., and Lee, H. C. (1993) Formation and hydrolysis of cyclic ADP-ribose by lymphocyte antigen CD38. Science 262,1056-1059）。这个结果在多个实验室的研究中得到了证实，从人类到鼠类的CD38都具有环化酶和水解酶的活性（Zocchi, E., Franco, L., Guida, L., Benatti, U., Bargellesi, A., Malavasi, F., Lee, El. C., and DeFlora, A. (1993) Single protein immunologically identified as CD38 displays NAD glycohydrolase and cyclic ADP-ribose hydrolase activities at the outer surface of human erythrocytes. Biochem. Bwphys. Res.Commun. 196, 1459-1465；Koguma, T., Takasawa, S., Tohgo, A., Karasawa, I., Furuya, Y., Yonekura, H., and Okamoto, H. (1994) Cloning and characterization of eDNA encoding rat ADP-ribosyl cyclase/cyclic ADP ribose hydrolase from islets of Langerbans. Biochim. Biophys. Acta 1223, 160-162；Takasawa, S., Tohgo, A., Noguchi, N., Koguma, T., Nata, K., Sugimoto, T., Yonekura, H., and Okamoto, H. (1993) Synthesis and hydrolysis of cyclic ADP-ribose by human leukocyte antigen CD38 and inhibition of the hydrolysis by ATP. J. Biol. Chem. 268,26052-26054；Tohgo, A., Takasawa, S., Noguchi, N., Koguma, T., Nata, K., Sugimoto, T.,Furuya, Y., Yonekura, H., and Okamoto, H. (1994) Essential cysteine residues for cyclic ADP-ribose synthesis and hydrolysis by CD38. J. Biol. Chem. 269, 28555-28557）。CD38分子中第119位和201位半胱氨酸（C119和C201）在海兔环化酶中没有对应的半胱氨酸残基，这两个残基对其水解酶活性很重要。因此，如果突变CD38分子的C119和/或C201 ，该酶将只具有环化酶活性；与之相反，如果引入突变K59C和E176G（对应于人CD38 的C119和C201，海兔环化酶将同时具有环化酶活性及水解酶活性（Tohgo, A., Takasawa, S., Noguchi, N., Koguma, T., Nata, K., Sugimoto, T.,Furuya, Y., Yonekura, H., and Okamoto, H. (1994) Essential cysteine residues for cyclic ADP-ribose synthesis and hydrolysis by CD38. J. Biol. Chem. 269, 28555-28557）。半胱氨酸残基不直接参与CD38的催化功能，但在保持其单体的催化活性结构方面有重要作用（Guida, L., Franco, L., Zocchi, E., and Dc Flora, A. (1995) Structural role of disulfide bridges in the cyclic ADP-ribose related bifunctional ectoenzyme CD38. FEBS Lett. 368,481-484）。CD38的催化反应是将NAD+转换为ADPR和尼克酰胺，不同于NADase（烟酰胺腺嘌呤二核苷酸激酶）催化的反应，它们都是利用NAD+为底物，形成的产物不同。由于在CD38催化的反应中很难检测cADPR， CD38曾被判定为典型的NADase。一类新的方法可以将CD38样的双功能酶同NADase区别开来。NGD（烟酰胺鸟嘌呤二核苷酸）能有效的显示出CD38的催化活性（Craeff, R. M., Walseth, T. F., Fryxell, K., Dale, W., Branton, W. D., and Lee, H. C.