Arruda Ana Paula, Nigro Mariana, Oliveira Gaya M, de Meis Leopoldo
From the Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Cidade Universitária, RJ, Brazil.
Biochim Biophys Acta. 2007 Jun;1768(6):1498-505. doi: 10.1016/j.bbamem.2007.03.016. Epub 2007 Mar 28.
The sarcoplasmic reticulum Ca(2+) ATPase 1 (SERCA 1) is able to handle the energy derived from ATP hydrolysis in such a way as to determine the parcel of energy that is used for Ca(2+) transport and the fraction that is converted into heat. In this work we measured the heat production by SERCA 1 in the two sarcoplasmic reticulum (SR) fractions: the light fraction (LSR), which is enriched in SERCA and the heavy fraction (HSR), which contains both the SERCA and the ryanodine Ca(2+) channel. We verified that although HSR cleaved ATP at faster rate than LSR, the amount of heat released during ATP hydrolysis by HSR was smaller than that measured by LSR. Consequently, the amount of heat released per mol of ATP cleaved (DeltaH(cal)) by HSR was lower compared to LSR. In HSR, the addition of 5 mM Mg(2+) or ruthenium red, conditions that close the ryanodine Ca(2+) channel, promoted a decrease in the ATPase activity, but the amount of heat released during ATP hydrolysis remained practically the same. In this condition, the DeltaH(cal) values of ATP hydrolysis increased significantly. Neither Mg(2+) nor ruthenium red had effect on LSR. Thus, we conclude that heat production by SERCA 1 depends on the region of SR in which the enzyme is inserted and that in HSR, the DeltaH(cal) of ATP hydrolysis by SERCA 1 depends on whether the ryanodine Ca(2+) channel is opened or closed.
肌浆网Ca(2+)ATP酶1（SERCA 1）能够以某种方式处理来自ATP水解的能量，从而确定用于Ca(2+)转运的能量份额以及转化为热量的部分。在这项工作中，我们测量了SERCA 1在两种肌浆网（SR）组分中的产热情况：富含SERCA的轻组分（LSR）和同时含有SERCA和兰尼碱Ca(2+)通道的重组分（HSR）。我们证实，尽管HSR比LSR更快地裂解ATP，但HSR在ATP水解过程中释放的热量比LSR测量的要少。因此，与LSR相比，HSR每摩尔裂解的ATP释放的热量（ΔH(cal)）更低。在HSR中，添加5 mM Mg(2+)或钌红（这两种条件会关闭兰尼碱Ca(2+)通道）会导致ATP酶活性降低，但ATP水解过程中释放的热量实际上保持不变。在这种情况下，ATP水解的ΔH(cal)值显著增加。Mg(2+)和钌红对LSR均无影响。因此，我们得出结论，SERCA 1的产热取决于该酶所插入的SR区域，并且在HSR中，SERCA 1水解ATP的ΔH(cal)取决于兰尼碱Ca(2+)通道是开放还是关闭。
