Cecchini G, Perl M, Lipsick J, Singer T P, Kearney E B
J Biol Chem. 1979 Aug 10;254(15):7295-301.
Riboflavine uptake and membrane-associated riboflavin-binding activity has been investigated in Bacillus subtilis. Riboflavin uptake proceeds via a system whose general properties are indicative of a carrier-mediated process: it is inhibited by substrate analogues, exhibits saturation kinetics, and is temperature-dependent. The organism concentrates riboflavin primarily as the phosphorylated cofactors FMN and FAD. Energy is required for uptake but whether the energy demand is required for both uptake and phosphorylation or only for the phosphorylation step is not known. Membrane-associated binding activity for riboflavin has also been demonstrated in membrane vesicles prepared from B. subtilis, and the binding component can be "solubilized" with Triton X-100. Evidence supporting the function of the binding component in riboflavin uptake by the intact cells includes the following. (i) Riboflavin analogues inhibit binding and uptake to nearly the same extent and with similar specificity of action. (ii) The KD for riboflavin-binding and the Km for uptake are in the same range. Similarly the Ki determined for the inhibitory analogue 5-deazariboflavin in the uptake assay and the KD for its interaction with the riboflavin-binding component of membrane vesicles are in the same range. (iii) Uptake in cells and binding in vesicles vary in the same direction with differences in growth conditions.
已对枯草芽孢杆菌中的核黄素摄取及与膜相关的核黄素结合活性进行了研究。核黄素摄取通过一个系统进行，该系统的一般特性表明是一个载体介导的过程：它受到底物类似物的抑制，表现出饱和动力学，并且依赖于温度。该生物体主要将核黄素浓缩为磷酸化的辅因子黄素单核苷酸（FMN）和黄素腺嘌呤二核苷酸（FAD）。摄取需要能量，但能量需求是用于摄取和磷酸化两者还是仅用于磷酸化步骤尚不清楚。在由枯草芽孢杆菌制备的膜囊泡中也已证明了与膜相关的核黄素结合活性，并且结合成分可以用曲拉通X - 100“溶解”。支持完整细胞摄取核黄素过程中结合成分功能的证据如下：（i）核黄素类似物抑制结合和摄取的程度几乎相同，且作用特异性相似。（ii）核黄素结合的解离常数（KD）和摄取的米氏常数（Km）在相同范围内。同样，在摄取测定中确定的抑制性类似物5 - 脱氮核黄素的抑制常数（Ki）及其与膜囊泡核黄素结合成分相互作用的KD在相同范围内。（iii）细胞摄取和囊泡结合随生长条件的差异在相同方向上变化。
