Prager N A, Suzuki T, Jaffe A S, Sobel B E, Abendschein D R
Cardiovascular Division, Washington University, Saint Louis, Missouri.
J Am Coll Cardiol. 1992 Aug;20(2):414-9. doi: 10.1016/0735-1097(92)90111-y.
This study was designed to characterize the nature and time course of carboxy-terminal lysine cleavages from the tissue isoform of MB creatine kinase (CK) in vivo.
Rapid conversion of the tissue isoform of MM CK to two additional circulating isoforms with one or both carboxy-terminal lysines cleaved facilitates early detection of new tissue isoform release after acute myocardial infarction and coronary recanalization. Characterization of changes in plasma MB CK isoform profiles, potentially enhancing specificity even further, has been hindered by difficulties in separating the isoform products and elucidation of carboxy-terminal lysine cleavages underlying their formation.
Isoform species with carboxy-terminal lysine present on B-monomers were separated from those from which lysine had been cleaved by anion exchange chromatography. Carboxy-terminal lysine on M-monomers was assayed with the use of a monospecific antibody.
MB CK in four pooled plasma samples from among 77 normal subjects exhibited carboxy-terminal lysine on 48 +/- 21% (mean +/- SEM) of B-monomers and 82 +/- 12% of M-monomers. Within the 1st 16 h after the onset of acute myocardial infarction, virtually all M- and B-monomers exhibited carboxy-terminal lysine, indicating release into plasma and the lack of rapid cleavage of lysine from the tissue isoform. After 20 to 30 h, 43 +/- 9% (three pools from 19 patients) of B-monomers and 95 +/- 10% of M-monomers exhibited lysine at the carboxyl terminus. After 40 to 50 h, 13 +/- 13% (four pools from 34 patients) of B-monomers and 46 +/- 19% of M-monomers still retained carboxy-terminal lysine.
In contrast to MM CK, the tissue isoform of MB CK undergoes slow cleavage of lysine from both monomers in vivo. Sequential cleavage of lysine first from the carboxyl terminus of B-monomers and subsequently from M-monomers is consistent with generation of at least two additional isoforms. Development of assays capable of resolving all of the isoforms of MB CK that can occur in vivo might increase sensitivity for early detection of new tissue isoform release associated with acute myocardial infarction and coronary recanalization compared with currently available assays that resolve only two species.
本研究旨在描述肌酸激酶同工酶MB（CK）组织亚型的羧基末端赖氨酸在体内的裂解性质和时间进程。
MM CK的组织亚型快速转化为另外两种循环亚型，其一个或两个羧基末端赖氨酸被裂解，这有助于急性心肌梗死和冠状动脉再通后新组织亚型释放的早期检测。血浆MB CK同工酶谱变化的特征描述，可能会进一步提高特异性，但由于难以分离同工酶产物以及阐明其形成背后的羧基末端赖氨酸裂解情况而受到阻碍。
通过阴离子交换色谱法将B亚基上存在羧基末端赖氨酸的同工酶与赖氨酸已被裂解的同工酶分离。使用单特异性抗体检测M亚基上的羧基末端赖氨酸。
77名正常受试者的四份混合血浆样本中的MB CK，48±21%（均值±标准误）的B亚基和82±12%的M亚基存在羧基末端赖氨酸。在急性心肌梗死发作后的最初16小时内，几乎所有的M亚基和B亚基都存在羧基末端赖氨酸，这表明其释放到血浆中且组织亚型的赖氨酸未快速裂解。20至30小时后，43±9%（来自19名患者的三个样本池）的B亚基和95±10%的M亚基在羧基末端存在赖氨酸。40至50小时后，13±13%（来自34名患者的四个样本池）的B亚基和46±19%的M亚基仍保留羧基末端赖氨酸。
与MM CK不同，MB CK的组织亚型在体内两个亚基的赖氨酸均发生缓慢裂解。赖氨酸先从B亚基的羧基末端依次裂解，随后从M亚基裂解，这与至少另外两种同工酶的产生一致。与目前仅能分辨两种同工酶的检测方法相比，开发能够分辨体内可能出现的所有MB CK同工酶的检测方法，可能会提高急性心肌梗死和冠状动脉再通相关新组织亚型释放早期检测的灵敏度。
