Beever R E, Burns D J
J Bacteriol. 1977 Nov;132(2):520-5. doi: 10.1128/jb.132.2.520-525.1977.
The phosphate uptake rate of Neurospora crassa germlings growing exponentially in media containing phosphate at concentrations between 10 mM and 50 micronM was virtually constant. The uptake characteristics of these germlings were studied in detail assuming the simultaneous operation of two uptake systems, one of low affinity and one of high affinity. The Km of the low-affinity system was constant after growth at phosphate concentrations greater than 1 mM but became progressively lower as the concentration was reduced below 1 mM. In contrast, the Km of the high-affinity system was independent of the phosphate concentration of the growth medium. The Vmax of each system was highest after growth at low phosphate concentrations. As the phosphate concentration was increased to a maximum of 100 mM, the Vmax of the low-affinity system fell gradually, whereas that of the high-affinity system at first fell rapidly but then reached a constant minimum value at concentrations of 2.5 mM and higher. The differences in the kinetic parameters fully account for the constancy of uptake rate shown by the germlings.
在含有浓度介于10 mM和50 μM之间磷酸盐的培养基中呈指数生长的粗糙脉孢菌幼苗，其磷酸盐摄取速率实际上是恒定的。假设存在两个摄取系统同时运作，一个是低亲和力系统，另一个是高亲和力系统，对这些幼苗的摄取特性进行了详细研究。在磷酸盐浓度大于1 mM的条件下生长后，低亲和力系统的Km是恒定的，但当浓度降至1 mM以下时，Km逐渐降低。相比之下，高亲和力系统的Km与生长培养基中的磷酸盐浓度无关。每个系统的Vmax在低磷酸盐浓度下生长后最高。当磷酸盐浓度增加到最大100 mM时，低亲和力系统的Vmax逐渐下降，而高亲和力系统的Vmax起初迅速下降，但在浓度达到2.5 mM及更高时达到一个恒定的最小值。动力学参数的差异完全解释了幼苗所表现出的摄取速率的恒定性。
