Bramucci M, Miano A, Quassinti L, Maccari E, Murri O, Amici D
Department of Molecular, Cellular and Animal Biology, University of Camerino, Via F Camerini, 2, I-62032 Camerino (MC), Italy.
Regul Pept. 2003 Mar 28;111(1-3):199-205. doi: 10.1016/s0167-0115(02)00284-7.
The degradation of thymic humoral factor-gamma2 (THF-gamma2), an immunoregulatory octapeptide important for T-lymphocyte regulation, by enzymes present in human plasma, was investigated. THF-gamma2 was metabolized through two steps that involved the detaching of N-terminal amino acid leucine followed by hydrolysis of the Lys(6)-Phe(7) bond. The THF-gamma2 cleavages were sensitive to aminopeptidase and metalloproteinase inhibitors. The degradation was completely blocked by amastatin and specific inhibitors of angiotensin converting enzyme (ACE). The cleavages occurred independently, with two different kinetics, faster for the N-terminal hydrolysis than for that of the Lys(6)-Phe(7) bond. Purified human plasma ACE was used to characterize the hydrolysis of Lys(6)-Phe(7) bond. The K(m) and K(cat) values for THF-gamma2 hydrolysis were 0.273 mM and 107 s(-1), respectively. The optimum of chloride concentration was 300 mM, while that of pH was 7.6. The presence of ACE in circulating mononuclear cells raises the possibility that it may play a role in modulating the THF-gamma2 activity.
研究了人血浆中存在的酶对胸腺体液因子-γ2（THF-γ2）的降解作用，THF-γ2是一种对T淋巴细胞调节很重要的免疫调节八肽。THF-γ2通过两个步骤进行代谢，首先是N端氨基酸亮氨酸的脱离，随后是Lys(6)-Phe(7)键的水解。THF-γ2的裂解对氨肽酶和金属蛋白酶抑制剂敏感。氨甲酰抑制剂和血管紧张素转换酶（ACE）的特异性抑制剂可完全阻断降解。裂解以两种不同的动力学独立发生，N端水解比Lys(6)-Phe(7)键的水解更快。使用纯化的人血浆ACE来表征Lys(6)-Phe(7)键的水解。THF-γ2水解的K(m)和K(cat)值分别为0.273 mM和107 s(-1)。氯化物浓度的最佳值为300 mM，而pH的最佳值为7.6。循环单核细胞中存在ACE增加了其可能在调节THF-γ2活性中发挥作用的可能性。
