Abstract
Six malformin B's produced by Aspergillus niger van Tiegh. were separated by HPLC. Their structures determined by the methods of amino acid analyses, mass spectrometry, and two-dimensional NMR were revealed as cyclic pentapeptides structurally related to malformin $A_1$. Both the NMR and MS/MS data suggest that the respective structures of separated malformin B's were as follows; cyclo-D-Cys-D-Cys-L-Val-D-Leu-L-allo-Ile for $B_{1a}$, cyclo-D-Cys-D-Cys-L-Val-D-Leu-L-Leu for $B_{1b}$, cyclo-D-Cys-D-Cys-L-Val-D-Val-L-Leu for $B_2$, cyclo-D-Cys-D-Cys-L-Val-D-Ile-L-Leu for $B_3$, cyclo-D-Cys-D-Cys-L-Val-D-Ile-L-Ile for $B_4$, and cyclo-D-Cys-D-Cys-L-Val-D-Val-L-Ile for $B_5$. Among the malformin B's, the structure of $B_{1b}$ was the same as that of malformin $A_3$ or C. All the malformin B's showed physiological activities in the two assay systems using corn(Zea mays L.) roots and mung bean(Phaseolus aureus Roxb.) hypercotyl segments. The malformin B's with molecular weight 529 were more effective for inducing corn root curvature than those with molecular weight 515. The difference in molecular weight of malformin B's, i.e., the retention time on HPLC, results in the polarity change of the whole malformin molecule which affects the revealation of the malformin activities. In addition, the disulfide form of the malformin B's gives the rigidity of the molecule, whereas the combination of the fourth and the fifth amino acid residues provides the optimal three-dimensional configuration to the malformin receptor of plants. Presumably, these two factors are appeared to be essential for the greatest physiological activity of malformin B's. malformin $B_{1a}$ caused the corn root curvature by 90% at a concentration of $0.25{\mu}M$. However, such differential activities with molecular weight of 529 or 515 of malformin B's were not found in the mung bean hypercotyl segment test. Maximum stimulation of mung bean hypercotyl growth was observed at $0.1{\mu}M$ concentration of malformin B's. The growth of the segments treated with $B_5$ was 154% greater than that of the control.
말포민 B로부터 신규의 $B_3$, $B_4$ 및 $B_5$를 포함한 6종의 B동족체들이 단리 구조결정되었다. 본 연구에 의해 말포민 B동족체의 화학구조는, $B_{1a}$(1)가 cyclo-D-Cys-D-Cys-L-Val-D-Leu-L-allo-Ile, $B_{1b}$(2)가 cyclo-D-Cys-D-Cys-L-Val-D-Leu-L-Leu, $B_2$(3)가 cyclo-D-Cys-D-Cys-L-V al-D-Val-L-Leu, $B_3$(4)가 cyclo-D-Cys-D-Cys-L-Val-D-Ile-L-Leu, $B_4$(5)가 cyclo-D-Cys-D-Cys-L-Val-D-Ile-L-Ile, $B_5$(6)가 cyclo-D-Cys-D-Cys-L-Val-D-Val-L-Ile으로서 확정되었다. B's, $B_{1b}$ C 이들 중, 말포민 $B_{1b}$(2)의 화학구조는 말포민 $A_3$ 및 말포민 C와 동일한 것으로 판명되었다. 단리된 말포민 B동족체에 대해서 옥수수 근부굴곡활성과 녹두 상배축산장활성을 지표로 하여 생물검정을 실시한 결과, 모든 B동족체가 활성을 나타내었다. 옥수수 근부굴곡활성의 검정으로부터, 분자량 529의 동족체가 분자량 515의 동족체보다 높은 활성을 보여주었으며, 이는 HPLC상의 retention time에서 확인된 바와 같이, 전체 말포민분자의 극성 이 옥수수 근부굴곡활성에 대해서 영향을 마친다는 사실을 시사한다. 또한, 말포민의 구조를 유지시켜주는 -S-S-가교구조와 제4-제5 아미노산 잔기에 측쇄구조가 상이한 leucine과 isoleucine의 조합이 말포민 수용부위와의 결합에 있어서 최적의 형상을 취할 수 있다는 점에서 말포민류의 활성 발현에 중요한 구조적 요소들일 것으로 추정되어진다. 말포민 $B_{1a}$는 $0.25{\mu}m$에서 90%의 옥수수 근부굴곡활성을 나타내었다. 그러나, 녹두 상배축산장활성의 경우 분자량에 따른 활성의 차이는 인정되지 않았으며, 말포민 $B_5$의 처리시 $0.1{\mu}m$에서 대조구에 비해 1.54%의 신장촉진을 보여주었다.
