Ihara H, Kuroda E, Wadano A, Himeno M
a Department of Agricultural Chemistry, College of Agriculture , University of Osaka Prefecture , Sakai, Osaka 591 , Japan.
Biosci Biotechnol Biochem. 1993 Jan;57(2):200-4. doi: 10.1271/bbb.57.200.
Two δ-endotoxins, CryIA(a) and CryIA(b), from Bacillus thuringiensis subsp.. aizawai were used to investigate the specificity in insecticidal activity. CryIA(a) was 17-fold more toxic to Bomhyx mori than CryIA(b). After in vitro solubilization and digestion of these δ-endotoxins, the specificity of toxicity was retained. Trypsin-activated CryIA(a) and CryIA(b) showed specific, high affinity and saturable binding to brush border membrane vesicles (BBMV) from B. mori midguts. These two toxins competed for the same binding site. Dissociation constant for CryIA(a) and CryIA(b) binding to B. mori BBMV was O.89nM and 1.46 nM, respectively. In both toxins, dissociation reaction followed a biphasic process with a fast and a very slow component, suggesting that binding of the toxins proceeds through a reversible component and an apparently irreversible component. In the CryIA(a) dissociation reaction, the irreversible component comprised a large portion of total binding. On the other hand in that of CryIA(b), the reversible component was major. These results suggest that the specific toxicity of the toxins to B. mori may depend mainly on irreversibility.
使用来自苏云金芽孢杆菌 aizawai 亚种的两种 δ-内毒素 CryIA(a) 和 CryIA(b) 来研究杀虫活性的特异性。CryIA(a) 对家蚕的毒性比 CryIA(b) 高 17 倍。在对这些 δ-内毒素进行体外溶解和消化后，毒性特异性得以保留。胰蛋白酶激活的 CryIA(a) 和 CryIA(b) 显示出与家蚕中肠刷状缘膜囊泡（BBMV）的特异性、高亲和力和饱和结合。这两种毒素竞争相同的结合位点。CryIA(a) 和 CryIA(b) 与家蚕 BBMV 结合的解离常数分别为 0.89 nM 和 1.46 nM。在这两种毒素中，解离反应均遵循双相过程，具有快速和非常缓慢的成分，这表明毒素的结合通过一个可逆成分和一个明显不可逆成分进行。在 CryIA(a) 的解离反应中，不可逆成分占总结合的很大一部分。另一方面，在 CryIA(b) 的解离反应中，可逆成分占主要部分。这些结果表明，毒素对家蚕的特异性毒性可能主要取决于不可逆性。
