Landeira-Fernandez A M, Galina A, Jennings P, Montero-Lomeli M, de Meis L
Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Cidade Universitária, 21941-590, Rio de Janeiro, Brazil.
Comp Biochem Physiol A Mol Integr Physiol. 2000 Jun;126(2):263-74. doi: 10.1016/s1095-6433(00)00197-5.
Although several Ca(2+)-ATPase isoforms have been described in vertebrates, little is known about Ca(2+)-transport in the muscle of invertebrates. In the microsomal fraction obtained from the sea cucumber (Ludwigothurea grisea) longitudinal body wall smooth muscle, we identified a Ca(2+)-transport ATPase that is able to transport Ca(2+) at the expense of ATP hydrolysis. This enzyme has a high affinity for both Ca(2+) and ATP, an optimum pH around 7.0, and - different from the vertebrate sarcoplasmic reticulum Ca(2+)-ATPases isoforms so far described - is activated 3- to 5-fold by K(+) but not by Li(+), at all temperatures, Ca(2+) and ATP concentrations tested. Calcium accumulation by the sea cucumber microsomes is inhibited by Mg/ATP concentrations >1 mM and the accumulated Ca(2+) is released to the medium when the ATP concentration is raised from 0.1 to 4.0 mM.
尽管在脊椎动物中已描述了几种钙（Ca²⁺）-ATP酶同工型，但关于无脊椎动物肌肉中的钙（Ca²⁺）转运却知之甚少。在从海参（Ludwigothurea grisea）纵体壁平滑肌获得的微粒体部分中，我们鉴定出一种钙（Ca²⁺）转运ATP酶，它能够以ATP水解为代价转运钙（Ca²⁺）。这种酶对钙（Ca²⁺）和ATP都具有高亲和力，最适pH约为7.0，并且与迄今为止描述的脊椎动物肌浆网钙（Ca²⁺）-ATP酶同工型不同，在所有测试的温度、钙（Ca²⁺）和ATP浓度下，它都被钾（K⁺）激活3至5倍，而不被锂（Li⁺）激活。当镁/ATP浓度>1 mM时，海参微粒体的钙积累受到抑制，并且当ATP浓度从0.1 mM提高到4.0 mM时，积累的钙（Ca²⁺）会释放到培养基中。
