Slemmon J R, Martzen M R
Department of Biochemistry, University of Rochester Medical Center, New York 14642.
Biochemistry. 1994 May 10;33(18):5653-60. doi: 10.1021/bi00184a039.
The calmodulin-binding polypeptide neuromodulin (GAP-43) was tested in vitro for its ability to modulate a typical calmodulin target, the enzyme nitric oxide synthase. The titration of enzyme with increasing neuromodulin concentrations demonstrated a concentration-dependent decrease in enzyme activity. Subsequent analysis of the ability of increased calcium concentrations to activate the enzyme was tested in the presence or absence of neuromodulin. The effect of neuromodulin on the calcium-dependent activation of the enzyme was to depress enzyme activity in the range of 0.2 to approximately 6 microM calcium. Treatment of the neuromodulin polypeptide with protein kinase C eliminated its ability to inhibit nitric oxide synthase activation. Subsequent treatment of the phosphorylated neuromodulin with calcineurin (phosphatase 2b) caused it to regain its inhibitory action on the enzyme. The results from these in vitro studies have indicated that neuromodulin has the ability to affect the activation of a calmodulin-dependent enzyme at levels of the polypeptide that exist in neurons. They also demonstrated that the regulation occurred within a physiological range of calcium concentrations. Since the inhibition of enzyme activity appeared to be occurring through the interaction of neuromodulin with calmodulin, it seems likely that neuromodulin has a general ability to impede activation of calmodulin-dependent targets.
对钙调蛋白结合多肽神经调制蛋白（GAP - 43）进行了体外测试，以检验其调节典型钙调蛋白靶点——一氧化氮合酶的能力。随着神经调制蛋白浓度增加对该酶进行滴定，结果显示酶活性呈浓度依赖性降低。随后，在有或无神经调制蛋白存在的情况下，测试了增加钙浓度激活该酶的能力。神经调制蛋白对该酶钙依赖性激活的影响是，在钙浓度为0.2至约6微摩尔范围内抑制酶活性。用蛋白激酶C处理神经调制蛋白多肽后，其抑制一氧化氮合酶激活的能力丧失。随后用钙调神经磷酸酶（磷酸酶2b）处理磷酸化的神经调制蛋白，使其恢复对该酶的抑制作用。这些体外研究结果表明，神经调制蛋白能够在神经元中存在的多肽水平上影响钙调蛋白依赖性酶的激活。研究还表明，这种调节发生在钙浓度的生理范围内。由于酶活性的抑制似乎是通过神经调制蛋白与钙调蛋白的相互作用发生的，因此神经调制蛋白似乎普遍具有阻碍钙调蛋白依赖性靶点激活的能力。
