Najm I, Vanderklish P, Etebari A, Lynch G, Baudry M
Section of Neurobiology, University of Southern California, Los Angeles 90089-2520.
J Neurochem. 1991 Oct;57(4):1151-8. doi: 10.1111/j.1471-4159.1991.tb08273.x.
Polyamine synthesis is induced by various extracellular signals, and it is widely held that this biochemical response participates in cell growth and differentiation. Certain of the triggers for synthesis in brain tissues also increase the breakdown of high-molecular-weight structural proteins, apparently by activating calcium-dependent proteases (calpains). The present experiments tested the possibility that calpain activity is modulated by polyamines. Spermine, spermidine, and putrescine all increased calcium-dependent proteolysis of [14C]casein by soluble fractions of rat brain. The order of potency was spermine greater than spermidine greater than putrescine, with apparent affinities of 30, 300, and 6,000 microM, respectively. Each of the three polyamines at physiological concentrations also potentiated the calcium-dependent breakdown of two endogenous high-molecular-weight structural proteins known to be substrates of calpain, in both supernatant and membrane fractions. The thiol protease inhibitor leupeptin, a known calpain inhibitor, also inhibited calcium-dependent proteolysis in the presence and absence of polyamines. The polyamines did not increase the activity of purified calpain I or calpain II determined with either [14C]casein or purified spectrin as the substrate, nor did they interfere with the inhibitory effects of calpastatin, an endogenous inhibitor of calpain. However, polyamines potentiated the stimulation of endogenous but not purified calpain activity produced by an endogenous calpain activator. These results suggest a role for polyamines in protein degradation as well as protein synthesis.
多胺合成由多种细胞外信号诱导，人们普遍认为这种生化反应参与细胞生长和分化。脑组织中某些合成触发因素也会增加高分子量结构蛋白的分解，显然是通过激活钙依赖性蛋白酶（钙蛋白酶）来实现的。本实验测试了钙蛋白酶活性受多胺调节的可能性。精胺、亚精胺和腐胺均可增加大鼠脑可溶性组分对[14C]酪蛋白的钙依赖性蛋白水解。效力顺序为精胺大于亚精胺大于腐胺，表观亲和力分别为30、300和6000微摩尔。在生理浓度下，这三种多胺中的每一种还增强了上清液和膜组分中两种已知为钙蛋白酶底物的内源性高分子量结构蛋白的钙依赖性分解。硫醇蛋白酶抑制剂亮抑酶肽是一种已知的钙蛋白酶抑制剂，在有或没有多胺的情况下也能抑制钙依赖性蛋白水解。多胺不会增加以[14C]酪蛋白或纯化血影蛋白为底物测定的纯化钙蛋白酶I或钙蛋白酶II的活性，也不会干扰钙蛋白酶内源性抑制剂钙蛋白酶抑制蛋白的抑制作用。然而，多胺增强了内源性钙蛋白酶激活剂对内源性而非纯化钙蛋白酶活性的刺激。这些结果表明多胺在蛋白质降解以及蛋白质合成中发挥作用。
