Sahin-Tóth M, Tóth M
Department of Physiology, University of California Los Angeles, Los Angeles, California 90095-1662, USA.
Biochem Biophys Res Commun. 2000 Aug 28;275(2):668-71. doi: 10.1006/bbrc.2000.3355.
The recent discovery that mutation Asn21 --> Ile in the human cationic trypsinogen (Tg) is associated with hereditary pancreatitis has brought into focus the functional role of amino acid 21 in mammalian Tgs. In the present paper, the effect of mutations Thr21 --> Asn and Thr21 --> Ile on the Ca(2+) dependence of zymogen activation was investigated, using the autolysis-resistant rat Tg mutant Arg117 --> His. In the absence of Ca(2+), rat Tg exhibited low but significant basal autoactivation, which was inhibited by micromolar concentrations of Ca(2+) (IC(50) 2.6 microM). Interestingly, basal autoactivation was diminished in both mutants, and no further inhibition by micromolar Ca(2+) was detectable. Millimolar Ca(2+) concentrations markedly and comparably stimulated autoactivation of wild-type and mutant zymogens (EC(50) 1.7-2.4 mM). The results indicate that rat Tg is subject to dual regulation by Ca(2+), allowing zymogen stabilization in a low-Ca(2+) environment and efficient activation in a high-Ca(2+) milieu.
最近发现人类阳离子胰蛋白酶原（Tg）中的Asn21→Ile突变与遗传性胰腺炎相关，这使得21位氨基酸在哺乳动物Tg中的功能作用成为焦点。在本文中，利用抗自溶大鼠Tg突变体Arg117→His，研究了Thr21→Asn和Thr21→Ile突变对酶原激活的Ca(2+)依赖性的影响。在无Ca(2+)的情况下，大鼠Tg表现出低但显著的基础自激活，其被微摩尔浓度的Ca(2+)抑制（IC(50) 2.6 microM）。有趣的是，两种突变体中的基础自激活均减弱，且未检测到微摩尔Ca(2+)的进一步抑制作用。毫摩尔浓度的Ca(2+)显著且同等程度地刺激野生型和突变型酶原的自激活（EC(50) 1.7 - 2.4 mM）。结果表明大鼠Tg受Ca(2+)的双重调节，使得酶原在低Ca(2+)环境中稳定，在高Ca(2+)环境中有效激活。
