Karlsson K, Marklund S L
Department of Clinical Chemistry, Umeå University Hospital, Sweden.
J Clin Invest. 1988 Sep;82(3):762-6. doi: 10.1172/JCI113676.
Extracellular-superoxide dismutase (EC-SOD) is heterogenous in the vasculature with regard to heparin affinity and can be separated into three fractions: A, without affinity; B, with weak affinity; and C, with relatively strong heparin affinity. The plasma clearance of intravenously injected 125I-labeled and unlabeled human EC-SOD C was studied in rabbits. About 90% of injected 125I-EC-SOD C was eliminated from the blood within 5-10 min. Injection of heparin after 10 or 20 min led to an immediate release of all sequestered 125I-EC-SOD C back to the blood plasma. Later injections of heparin led to diminished release, although release could still be demonstrated after 72 h. A half-time of approximately 10 h could be calculated for heparin-releasable 125I-EC-SOD C. Unlabeled EC-SOD C, determined as enzymic activity and with ELISA, was likewise sequestered and released to the same degree as 125I-labeled EC-SOD C by heparin as tested at 20 min and 5 h. The immediacy of the heparin-induced release indicates that the sequestered enzyme had been bound to endothelial cell surfaces. The length of the half-time suggests that the putative cell surface binding has a physiological function and is not primarily a step in enzyme degradation. The distribution of sequestered 125I-labeled EC-SOD C to different organs was determined at times between 10 min and 24 h. Of the organs, the liver contained the most 125I-EC-SOD C, followed by kidney, spleen, heart, and lung. At all investigated times, the content in the analyzed organs was nearly as large as the amount that could be promptly released to plasma by intravenous heparin. This indicates that almost all 125I-EC-SOD C in the organs was present on endothelial cell surfaces and was not bound by other tissue cell surfaces, or was present within the cells.
细胞外超氧化物歧化酶（EC-SOD）在脉管系统中，就肝素亲和力而言是异质性的，并且可以分为三个部分：A，无亲和力；B，弱亲和力；C，相对较强的肝素亲和力。对兔静脉注射125I标记和未标记的人EC-SOD C后的血浆清除情况进行了研究。静脉注射的125I-EC-SOD C约90%在5-10分钟内从血液中清除。在10或20分钟后注射肝素导致所有被隔离的125I-EC-SOD C立即释放回血浆。肝素的后续注射导致释放减少，尽管在72小时后仍可证明有释放。对于肝素可释放的125I-EC-SOD C，可以计算出约10小时的半衰期。通过酶活性测定和ELISA检测，未标记的EC-SOD C在20分钟和5小时时，与125I标记的EC-SOD C一样，被肝素隔离并释放到相同程度。肝素诱导释放的即时性表明，被隔离的酶已与内皮细胞表面结合。半衰期的时长表明，假定的细胞表面结合具有生理功能，而不是酶降解的主要步骤。在10分钟至24小时之间的不同时间点，测定了被隔离的125I标记的EC-SOD C在不同器官中的分布。在这些器官中，肝脏含有的125I-EC-SOD C最多，其次是肾脏、脾脏、心脏和肺。在所有研究时间点，分析器官中的含量几乎与静脉注射肝素后可迅速释放到血浆中的量一样大。这表明器官中几乎所有的125I-EC-SOD C都存在于内皮细胞表面，未被其他组织细胞表面结合，或不存在于细胞内。
