Pasantes-Morales H
Vision Res. 1982;22(12):1487-93. doi: 10.1016/0042-6989(82)90214-0.
Frog rod outer segments (ROS) isolated in a Ca-free, EGTA-containing medium, showed a rapid ATP-dependent accumulation of 45Ca, GTP, CTP, ITP, UTP, GMP and beta-, gamma-methylene ATP did not substitute for ATP in energizing Ca uptake. This process required Mg, it was abolished in the presence of Ca ionophores A23187 and X537A and is not affected by external sodium. The Arrhenius activation energy was 7.9 kcal/mol and the pH optimum was approximately 7.2. The apparent Km for Ca uptake was 66 microM with a V max of 12.5 nmol/mg protein. 45Ca accumulation was reduced in illuminated ROS. The presence of 5-25 mM taurine, but not of GABA, glycine, histidine or proline, markedly enhanced Ca uptake by ROS.
在不含钙、含有乙二醇双（2-氨基乙基醚）四乙酸（EGTA）的培养基中分离出的青蛙视杆细胞外段（ROS），显示出45Ca的快速ATP依赖性积累，鸟苷三磷酸（GTP）、胞苷三磷酸（CTP）、肌苷三磷酸（ITP）、尿苷三磷酸（UTP）、鸟苷一磷酸（GMP）和β-、γ-亚甲基ATP在为钙摄取供能时不能替代ATP。这个过程需要镁，在钙离子载体A23187和X537A存在时被消除，并且不受细胞外钠的影响。阿累尼乌斯活化能为7.9千卡/摩尔，最适pH约为7.2。钙摄取的表观米氏常数（Km）为66微摩尔，最大反应速度（V max）为12.5纳摩尔/毫克蛋白质。光照下的ROS中45Ca积累减少。5-25毫摩尔的牛磺酸存在时能显著增强ROS对钙的摄取，而γ-氨基丁酸（GABA）、甘氨酸、组氨酸或脯氨酸则不能。
