Johnson J D, Snyder C, Walsh M, Flynn M
Department of Medical Biochemistry, Ohio University Medical Center, Columbus 43210, USA.
J Biol Chem. 1996 Jan 12;271(2):761-7. doi: 10.1074/jbc.271.2.761.
Myosin light chain kinase and peptides from the calmodulin (CaM) binding domains of myosin light chain kinase (RS-20, M-13), CaM kinase II, and the myristoylated alanine-rich protein kinase C substrate protein slowed Ca2+ dissociation from CaM's N-terminal sites from 405 +/- 75/s to 1.8-2.9/s and from CaM's C-terminal sites from 2.4 +/- 0.2/s to 0.1-0.4/s at 10 degrees C. Since Ca2+ dissociates 5-29 times faster from the N-terminal in these CaM.peptide complexes and both lobes are required for activation, Ca2+ dissociation from the N-terminal would control target protein inactivation. Ca2+ binds 70 times faster to the N-terminal (1.6 x 10(8) M-1 s-1) than the C-terminal sites (2.3 x 10(6) M-1 s-1). In a 0.6-ms half-width Ca2+ transient, Ca2+ occupied > 70% of the N-terminal but only 20% of the C-terminal sites. RS-20 produced a 9-fold and CaM kinase II a 6.3-fold increase in C-terminal Ca2+ affinity, suggesting that some target proteins may be bound to the C-terminal at resting [Ca2+]. When this is the case, Ca2+ exchange with the faster N-terminal sites may regulate CaM's activation and inactivation of these target proteins during a Ca2+ transient.
肌球蛋白轻链激酶以及来自肌球蛋白轻链激酶（RS - 20、M - 13）、钙调蛋白依赖性蛋白激酶II和豆蔻酰化富含丙氨酸的蛋白激酶C底物蛋白的钙调蛋白（CaM）结合域的肽段，在10℃时将Ca2 +从CaM N端位点的解离速度从405±75 /秒减慢至1.8 - 2.9 /秒，从CaM C端位点的解离速度从2.4±0.2 /秒减慢至0.1 - 0.4 /秒。由于在这些CaM - 肽复合物中Ca2 +从N端解离的速度快5 - 29倍，且两个叶对于激活都是必需的，所以Ca2 +从N端的解离将控制靶蛋白的失活。Ca2 +与N端的结合速度（1.6×10⁸M⁻¹s⁻¹）比C端位点（2.3×10⁶M⁻¹s⁻¹）快70倍。在0.6毫秒半高宽的Ca2 +瞬变中，Ca2 +占据了> 70%的N端位点，但仅占据了20%的C端位点。RS - 20使C端Ca2 +亲和力增加了9倍，钙调蛋白依赖性蛋白激酶II使其增加了6.3倍，这表明一些靶蛋白在静息[Ca2 +]时可能与C端结合。在这种情况下，Ca2 +与更快的N端位点的交换可能在Ca2 +瞬变期间调节CaM对这些靶蛋白的激活和失活。
