Presence of protein polymorphism in karasurin, an abortifacient and anti-tumor protein, identified with physicochemical properties.

Karasurin is an abortifacient plant protein isolated from fresh root tubers of Trichosanthes kirilowii Maximowicz var. japonicum Kitamrra (Cucurbitaceae). This study describes the presence of protein polymorphism in karasurin (karasurin-A and karasurin-B) separated by ion-exchange chromatography. Two components showed no differences in the molecular weight (ca. 28000), the amino acid composition, the neutral sugar content and part of the amino acid sequence. A unique difference was observed in their isoelectric points (10.1 for karasurin-A and 10.2 for karasurin-B). However, modifications of glycosylation or phosphorylation were not found. Biological assays for inducing mid-term abortion in pregnant mice and inhibition of the growth of BeWo cells gave no significant differences between them. The presence of protein polymorphism in karasurin, whose biological significance is not yet understood, is a first finding among several abortifacient proteins.