半夏凝集素在脂双层形成的阳离子通道

半夏凝集素是从多年生植物三叶半夏的块茎鲜汁中分离纯化的糖结合蛋白,具凝集素活性,与甘露聚糖有专一结合。本工作利用双室系统观察了它对人工脂双层的作用。 人工脂双层由卵磷脂和胆固醇(重量比为4:1)的正癸烷溶液形成。电阻≥10GΩ。在电压箝位下将半夏凝集素(1—4μg/ml)加至系统的一小室,几分钟后即观察到通道样活动噪音,脂双层电阻下降。甘露聚糖对这种变化有明显的对抗作用,加入40μg/ml的甘露聚糖可使脂双层的膜电阻立即从2GΩ恢复到对照水平(≥10GΩ)。在低浓度半夏凝集素和低维持电压下可获得单位电导涨落记录。在100mmol/L对称KCl溶液中记录的半夏凝集素单通道电流的优势电导为35pS。通过测定在非对称盐溶液中的平衡电位,根据Goldman—Hodgkin—Katz电位方程可推算出通道的离子选择性。结果表明,半夏凝集素形成的通道为阳离子通道。

CATION CHANNELS FORMED IN LIPID BILAYER BY PINELLIA TERNATA LECTIN

Pinellia ternata lectin (PTL), a protein exhibiting hemagglutination activity and carbohydrate binding specificity to mannan was purified from rhizome of Pinellia ternata. In this work the actions of PTL on artificial lipid bilayer were investigated by means of the two-compartment system of Mueller and Rudin. The lipid bilayer with resistance more than 10G omega was formed by a solution of lecithin and cholesterol (20 mg/ml and 5 mg/ml respectively) in N-decane. The electrical properties of the lipid bilayer were investigated in voltage clamp mode. Several minutes after the addition of PTL (2 micrograms/ml) in one compartment the channel-like noise as well as a decrease of the resistance of the bilayer were observed. These actions were inhibited by mannan significantly. The resistance increase of the bilayer with PTL-channels could be observed from 2G omega to control level (greater than or equal to 10 G omega) immediately after addition of 40 micrograms/ml mannan. The discrete conduction steps were recorded at low concentration of PTL and at low holding potential. The predominant unit conductance was 35pS in symmetric KCl solution of 100 mmol/L. The selectivity of PTL-channel was estimated from Goldman-Hodgkin-Katz equation by measurement of the reversal potential in an asymmetrical salt solution. The results showed that PTL-channels were cation selective.