리보즘불활성화 단백질(Ribosome-inactivating protein, RIP)을 생성하는 식물을 탐색하여 그중 호박$(Cucurbita;moschata;D_{UCHESNE})$ 잎에서 ammonium sulfate 침전, DE 52-Cellulose, S-Sepharose, FPLC Superose 12 HR, FPLC Mono-S column chromatography에 의하여 ribosome-Inactivating 활성이 있는 단백질(PR 1, PRIP 2)을 분리하였다. 정제된 단백질의 분자량은 SDS-PAGE에서 약 31,000과 30,500인 염기성 단백질로서, 특히 PRIP 1은 열에도 안정하여 $50^{circ}C$에서 30분간 처리한 경우에도 활성이 유지되었다. 이 단백질들의 ribosome-inactivating 활성을 in vitro translation system에서 측정한 결과 50% 활성저해농도 $(IC_{50})$는 PRIP 1은 0.82nM, PRIP 2은 0.79 nM이었다. PRIP 1과 PRIP 2의 N-말단부분의 아미노산 서열을 분석하여, 이미 밝혀진 리보즘불활성화 단백질들과 아미노산서열의 유사성을 분석해 본 결과, PRIP 1은 Luffa cylindrica에서 분리된 Luffin B 및 Trichosanthes kirilowii Maximowicz에서 분리된 Trichokirin과, PRE 2은 Momordia charantia에서 분리된 Momordin II 및 MAP 30과 유사성이 매우 높았다.
Two ribosome-inactivating proteins, PRIP 1 and PRIP 2 have been isolated from the leaves of $Cucurbita;moschata;D_{UCHESNE}$. Crude extracts were purified through ammonium sulfate precipitation and column chromatography using DE-52 cellulose, S-Sepharose, FPLC Suprose 12 HR and FPLC Mono-S. The molecular weights of PRIP 1 and PRIP 2 were 31,000 and 30,500, respectively. PRIP 2 was thermostabe and maintained its activity even after the incubation of the protein at $50^{circ}C$ for 30 min. In a cell free in vitro translation system using rabbit reticulocyte lysate, protein synthesis was inhibited by the addition of PRIP 1 and PRIP 2. The $IC_{50}$ of PRIP 1 and PRIP 2 were 0.82 nM and 0.79 nM, respectively. The comparison of N-terminal amino acid sequences of the PRIP 1 and PRIP 2 with known RIPs revealed that PRIP 1 shows sequence similarity with Luffin B from Luffa cylindrica and Trichokirin from Trichosanthes kirilowii Maximowicz and PRH) 2 has sequence similarity with Momordin II and MAP 30 from Momordica charantia.
