Henz Sandra Liana, Fürstenau Cristina Ribas, Chiarelli Rafael Augusto, Sarkis João José Freitas
Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade Federal do Rio Grande do Sul, Rua Ramiro Barcelos 2600-Anexo,90035-003, Porto Alegre, RS, Brazil.
Arch Oral Biol. 2007 Oct;52(10):916-23. doi: 10.1016/j.archoralbio.2007.03.006. Epub 2007 May 17.
The participation of ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP) activity in the nucleotide hydrolysis by salivary gland cells of rats was evaluated using p-nitrophenyl 5'-thymidine monophosphate (p-Nph-5'-TMP) as a substrate for this enzyme. We investigated the biochemical characteristics of this ectoenzyme in cells cultured from submandibular salivary glands of rats. Primary cell cultures demonstrated ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP) activities, which could be observed by extracellular hydrolysis of p-Nph-5'-TMP and other biochemical characteristics such as dependence of metal ions, dependence of pH alkaline and inactivation by a metal ion chelator. The Km value for the hydrolysis of p-Nph-5'-TMP was 280.7+/-34.2 microM (mean+/-S.D., n=4) and Vmax was 721.31+/-225nmol p-nitrophenol/min/mg (mean+/-S.D., n=4). We suggest that E-NPP is co-localized with an ecto-ATP diphosphohydrolase/ecto-NTPDase and an ecto-5'-nucleotidase, since these enzymes probably act under different conditions. It may be postulated that the physiological role for these ecto-enzymes is to terminate the action of the co-transmitter ATP, generating adenosine.
使用对硝基苯基5'-胸苷单磷酸（p-Nph-5'-TMP）作为该酶的底物，评估了胞外核苷酸焦磷酸酶/磷酸二酯酶（E-NPP）活性在大鼠唾液腺细胞核苷酸水解中的参与情况。我们研究了从大鼠下颌下唾液腺培养的细胞中这种胞外酶的生化特性。原代细胞培养显示出胞外核苷酸焦磷酸酶/磷酸二酯酶（E-NPP）活性，这可以通过p-Nph-5'-TMP的细胞外水解以及其他生化特性如对金属离子的依赖性、对碱性pH的依赖性和金属离子螯合剂的失活来观察。p-Nph-5'-TMP水解的Km值为280.7±34.2微摩尔（平均值±标准差，n = 4），Vmax为721.31±225纳摩尔对硝基苯酚/分钟/毫克（平均值±标准差，n = 4）。我们认为E-NPP与胞外ATP二磷酸水解酶/胞外NTPDase和胞外5'-核苷酸酶共定位，因为这些酶可能在不同条件下起作用。可以推测这些胞外酶的生理作用是终止共递质ATP的作用，生成腺苷。
