Horn L W
J Membr Biol. 1986;89(2):185-92. doi: 10.1007/BF01869714.
It is shown that the axoplasmic composition of acidic and neutral amino acids can be controlled effectively by the method of internal dialysis. Direct assay for specific binding and measurement of diffusion coefficients in axoplasm show that there is no significant binding or compartmentalization of amino acids. The dependence of amino acid efflux on substrate concentration can be measured under well-defined, true steady-state conditions. The taurine efflux-concentration relation in the Myxicola giant axon conforms to a second-order Hill equation. This fact is consistent with either a cooperative process or a mechanism in which membrane translocation is not the rate-controlling step. The effluxes of taurine and glycine from squid axon are an order of magnitude smaller than in Myxicola. The efflux-concentration relations are essentially linear up to 200 mM substrate concentration. This result may be produced by specific transporters which have very high asymmetry, or by simple diffusive leak in the absence of specific transporters.
结果表明，通过内部透析法可以有效控制轴浆中酸性和中性氨基酸的组成。对轴浆中特异性结合的直接测定和扩散系数的测量表明，氨基酸不存在显著的结合或分隔现象。在明确界定的真实稳态条件下，可以测量氨基酸流出对底物浓度的依赖性。黏液虫巨型轴突中牛磺酸流出与浓度的关系符合二阶希尔方程。这一事实与协同过程或膜转运不是速率控制步骤的机制相一致。鱿鱼轴突中牛磺酸和甘氨酸的流出量比黏液虫中的小一个数量级。在底物浓度高达200 mM时，流出与浓度的关系基本呈线性。这一结果可能是由具有非常高不对称性的特异性转运体产生的，或者是在没有特异性转运体的情况下由简单的扩散泄漏产生的。
