Nixon R A
J Neurosci. 1986 May;6(5):1264-71. doi: 10.1523/JNEUROSCI.06-05-01264.1986.
The activity of calcium-activated neutral proteinases (CANPs) toward endogenous substrates was measured in axons of retinal ganglion cell (RGC) neurons and separately in adjacent optic glia under in vitro conditions that preserved the ultrastructure and anatomic relationships between these cellular elements. RGC neurons and optic glia both expressed CANP activity. In contrast to RGC axons, which contained at least two CANP activities with calcium requirements in the millimolar (CANP A) and micromolar (CANP B) range (Nixon et al., 1985), CANP activity in optic glia was detectable only at millimolar calcium concentrations. When maximally activated, CANP(s) in optic glia exhibited a broad specificity for endogenous proteins but degraded larger proteins at a faster rate. The cytoskeletal protein fodrin (brain spectrin) was among the most susceptible endogenous substrates in RGC axons or glia. The similar properties of fodrin in neurons and glia, including its susceptibility to a purified millimolar calcium-sensitive brain CANP (mCANP), provided the basis for using this protein as a substrate to compare the relative activity of neuronal and glial CANPs in situ. Fodrin degradation mediated by CANPs proceeded at least 6 X more rapidly in intact RGC axons than in optic glia. Comparable differences in the relative degradation rates of the total neuronal and glial protein pools were also observed. These results indicate that the potential activity of CANPs is substantially greater in RGC neurons than in glia. The enormous potential activity and preferential localization of multiple CANP activities in RGC neurons support previously hypothesized roles for CANPs in the processing of axonally transported proteins and in the regulation of neuronal cytoskeletal dynamics and geometry.(ABSTRACT TRUNCATED AT 250 WORDS)
在体外条件下，在保留视网膜神经节细胞（RGC）神经元轴突以及相邻视神经胶质细胞超微结构和解剖关系的情况下，测量了钙激活中性蛋白酶（CANP）对内源性底物的活性。RGC神经元和视神经胶质细胞均表达CANP活性。与含有至少两种钙需求分别在毫摩尔（CANP A）和微摩尔（CANP B）范围的CANP活性的RGC轴突不同（尼克松等人，1985年），视神经胶质细胞中的CANP活性仅在毫摩尔钙浓度下才可检测到。当被最大程度激活时，视神经胶质细胞中的CANP对内源性蛋白质表现出广泛的特异性，但降解较大蛋白质的速度更快。细胞骨架蛋白血影蛋白（脑血影蛋白）是RGC轴突或胶质细胞中最易受影响的内源性底物之一。血影蛋白在神经元和胶质细胞中的相似特性，包括其对纯化的毫摩尔钙敏感脑CANP（mCANP）的敏感性，为使用该蛋白作为底物来比较原位神经元和胶质细胞CANP的相对活性提供了基础。由CANP介导的血影蛋白降解在完整的RGC轴突中进行的速度至少比视神经胶质细胞快6倍。在总神经元和胶质细胞蛋白库的相对降解率上也观察到了类似差异。这些结果表明，CANP在RGC神经元中的潜在活性远高于胶质细胞。RGC神经元中多种CANP活性的巨大潜在活性和优先定位支持了之前关于CANP在轴突运输蛋白加工以及神经元细胞骨架动力学和形态调节中的作用的假设。（摘要截短于250字）
