Interactions of viscotoxins with vesicles of genuine plant membranes.

Extracts of Viscum album L. produced by a specific homogenization procedure contain viscotoxins (VT) and liposome-like membrane vesicles, formed from cellular membranes. Interactions between these membrane structures and viscotoxins are characterized in this work. Binding properties of viscotoxins with mistletoe extracts or isolated membrane vesicles were analyzed by gel permeation chromatography (GPC) and centrifugation, followed by HPLC/UV for viscotoxin detection. The experiments show that a part of the viscotoxins is bound to membrane vesicles, and that this binding to the membrane structures is reversible. In the case of the vesicles studied from an extract of 100 mg plant material per mL (0.30 mM phospholipids, 244 microg/mL VT), 64 microg/mL VTs are bound to the membranes. The binding properties of the viscotoxin isoforms are different. VTA3 clearly binds more intensively to membrane structures than VTA2 or VTA1. Possible interaction of viscotoxins with DNA, which is also discussed as a mechanism of viscotoxin action, could be shown to be negligible in the framework of these experiments.