de Meis Leopoldo, Oliveira Gaya M, Arruda Ana Paula, Santos Reinaldo, Costa Rodrigo Madeiro da, Benchimol Marlene
Instituto de Bioquímica Médica, Prédio do CCS, Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro, Brazil.
IUBMB Life. 2005 Apr-May;57(4-5):337-45. doi: 10.1080/15216540500092534.
The Ca2+-ATPase (SERCA) found in vesicles derived from the sarco/endoplasmic reticulum vesicles of rats brown adipose tissue and rabbit white muscle were identified by gel electrophoresis, Western blot, electron microscopy and immunolabeling with gold particles. In both tissues, the isoform found was SERCA 1. The Ca2+ affinity of the fat SERCA 1 was different from the muscle isoform. The degree of uncoupling is estimated measuring the ratio between Ca2+ transport and ATP cleaved. In brown fat vesicles the degree of uncoupling varied depending on the Ca2+ concentration of the medium. This was not observed in vesicles derived from muscle. At all Ca2+ concentrations tested, the uncoupling was not related to Ca2+ leakage from the membrane and was far more pronounced in fat than in muscle vesicle. When a Ca2+ gradient was formed across the vesicles membrane the heat released during ATP hydrolysis varied between 22 and 26 Kcal/mol in both fat and muscle vesicles but in the absence of a gradient the heat released was 17 Kcal/mol in fat and 12 Kcal/mol in muscle. The data reported indicate that the SERCA 1 of brown adipocytes is far more thermogenic than the white muscle SERCA 1, and suggest that, in addition to storing Ca2+ inside the endoplasmic reticulum, the SERCA 1 may represent a source of heat production contributing to the thermogenic function of brown adipose tissue.
通过凝胶电泳、蛋白质免疫印迹、电子显微镜以及金颗粒免疫标记，鉴定了源自大鼠棕色脂肪组织和兔白色肌肉的肌浆网/内质网囊泡中的Ca2+-ATP酶（SERCA）。在这两种组织中，发现的同工型均为SERCA 1。脂肪组织的SERCA 1与肌肉组织的同工型对Ca2+的亲和力不同。通过测量Ca2+转运与ATP裂解之间的比率来估算解偶联程度。在棕色脂肪囊泡中，解偶联程度随培养基中Ca2+浓度的变化而变化。而在源自肌肉的囊泡中未观察到这种现象。在所有测试的Ca2+浓度下，解偶联均与膜上的Ca2+泄漏无关，并且在脂肪囊泡中比在肌肉囊泡中更为明显。当在囊泡膜上形成Ca2+梯度时，脂肪和肌肉囊泡中ATP水解过程中释放的热量在22至26千卡/摩尔之间变化，但在没有梯度的情况下，脂肪中释放的热量为17千卡/摩尔，肌肉中为12千卡/摩尔。所报道的数据表明，棕色脂肪细胞的SERCA 1比白色肌肉的SERCA 1产热得多，这表明，除了在内质网中储存Ca2+外，SERCA 1可能是棕色脂肪组织产热功能的一个产热来源。
