Strobel G A
Department of Plant Pathology, Montana State University, Bozeman, Mont. 59715.
Proc Natl Acad Sci U S A. 1974 Oct;71(10):4232-6. doi: 10.1073/pnas.71.10.4232.
The toxin-binding protein of sugarcane susceptible to eyespot disease also possesses raffinose-binding activity. The K(m)'s for binding are: helminthosporoside (toxin) 6.8 x 10(-5) M, raffinose 2.5 x 10(-5) M, and melibiose 2.6 x 10(-5) M. Evidence obtained by administering [(14)C]raffinose to sugarcane protoplasts suggests that this protein participates in alpha-galactoside transport. Cells from a resistant clone of sugarcane do not possess an active-binding protein, and likewise, do not actively take up raffinose. Interestingly, the K(+), Mg(++) ATPase (ATP phosphohydrolase, EC 3.6.1.3.) on the plasma membrane of the susceptible sugarcane is 30% activated by the toxin at 3 mM. In addition, toxin-treated tissue slices show a rapid uptake of (86)Rb(+)-K(+) which is in agreement with the toxin activation of the membrane K(+), Mg(++) ATPase. Since the ATPase does not directly interact with the toxin, the activation effect occurs by means of the toxin-binding protein. Membrane proteins may be influenced by the toxin-binding protein acting by one of several different mechanisms.
易患眼斑病的甘蔗的毒素结合蛋白也具有棉子糖结合活性。结合的米氏常数（K(m)）分别为：蠕孢糖苷（毒素）6.8×10⁻⁵M、棉子糖2.5×10⁻⁵M和蜜二糖2.6×10⁻⁵M。给甘蔗原生质体施用[¹⁴C]棉子糖所获得的证据表明，该蛋白参与α-半乳糖苷转运。来自甘蔗抗性克隆的细胞不具有活性结合蛋白，同样也不主动摄取棉子糖。有趣的是，在3 mM时，易感甘蔗质膜上的K⁺、Mg²⁺ATP酶（ATP磷酸水解酶，EC 3.6.1.3.）被毒素激活30%。此外，经毒素处理的组织切片显示对⁸⁶Rb⁺-K⁺的快速摄取，这与膜K⁺、Mg²⁺ATP酶的毒素激活作用一致。由于ATP酶不直接与毒素相互作用，激活作用是通过毒素结合蛋白发生的。膜蛋白可能受毒素结合蛋白通过几种不同机制之一的作用影响。
