Ziganshin A U, Ziganshina L E, King B E, Burnstock G
Department of Anatomy and Developmental Biology University College London, UK.
Pflugers Arch. 1995 Jan;429(3):412-8. doi: 10.1007/BF00374157.
Ecto-ATPase activity of Xenopus oocytes was studied by measuring the production of inorganic phosphate (Pi) from the breakdown of extracellular ATP. Enzyme activity involved Ca2+/Mg(2+)-dependent and Ca2+/Mg(2+)-independent dephosphorylation of ATP. Ca2+/Mg(2+)-dependent ecto-ATPase was active over a limited range of 0.01-1.0 mM ATP, while Ca2+/Mg(2+)-independent ATPase activity was active over a range of 0.1-30 mM ATP. Total enzyme activity was insensitive to changes in buffer pH (pH 7.0-9.0), but increased in a relatively linear manner with: (1) time of reaction (0-90 min), (2) number of cells (1-20 oocytes), and (3) temperature (10-37 degrees C). Ecto-ATPase activity was unaffected by ouabain (100 microM), sodium azide (100 microM), and oligomycin (5 micrograms/ml) (as inhibitors of endo-ATPases) and beta-glycerophosphate (10 mM) and p-nitrophenyl phosphate (10 mM) (as inhibitors of non-specific alkaline phosphatase). Total ecto-ATPase activity was reduced significantly in defolliculated oocytes, suggesting that the enzyme was located mainly on the enveloping follicle cell layer. The range order of preferential substrates was: ATP>GTP, ITP, UTP, CTP, TTP, 2-methylthioATP>ADP, 2-methylthioADP, AMP>>alpha, beta-methylene ATP, beta, gamma-methylene ATP, in the presence of divalent ions (where G is guanosine, I is inosine, U is uridine, C is cytidine and T is ribosylthymine). The P2-purinoceptor antagonist suramin [8-(3-benzamido-4-methylbenzamido)napthalene-1,3,5-trisul phonic acid), 100 microM] significantly inhibited total ecto-ATPase activity; this inhibition was competitive for the Ca2+/Mg(2+)-dependent enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)
通过测量细胞外ATP分解产生的无机磷酸（Pi），研究了非洲爪蟾卵母细胞的胞外ATP酶活性。酶活性涉及ATP的Ca2+/Mg(2+)依赖性和Ca2+/Mg(2+)非依赖性去磷酸化。Ca2+/Mg(2+)依赖性胞外ATP酶在0.01 - 1.0 mM ATP的有限范围内具有活性，而Ca2+/Mg(2+)非依赖性ATP酶活性在0.1 - 30 mM ATP范围内具有活性。总酶活性对缓冲液pH值（pH 7.0 - 9.0）的变化不敏感，但随以下因素以相对线性的方式增加：（1）反应时间（0 - 90分钟），（2）细胞数量（1 - 20个卵母细胞），以及（3）温度（10 - 37摄氏度）。胞外ATP酶活性不受哇巴因（100 microM）、叠氮化钠（100 microM）和寡霉素（5微克/毫升）（作为内膜ATP酶的抑制剂）以及β-甘油磷酸（10 mM）和对硝基苯磷酸（10 mM）（作为非特异性碱性磷酸酶的抑制剂）的影响。去滤泡卵母细胞中的总胞外ATP酶活性显著降低，这表明该酶主要位于包围滤泡的细胞层上。在二价离子存在的情况下（其中G是鸟苷，I是次黄苷，U是尿苷，C是胞苷，T是核糖胸腺嘧啶），优先底物的顺序为：ATP>GTP、ITP、UTP、CTP、TTP、2-甲硫基ATP>ADP、2-甲硫基ADP、AMP>>α,β-亚甲基ATP、β,γ-亚甲基ATP。P2嘌呤受体拮抗剂苏拉明[8-(3-苯甲酰胺基-4-甲基苯甲酰胺基)萘-1,3,5-三磺酸]，100 microM显著抑制总胞外ATP酶活性；这种抑制对Ca2+/Mg(2+)依赖性酶具有竞争性。（摘要截短于250字）
