Ngai P H K, Ng T B
Department of Biochemistry, Faculty of Medicine, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
Peptides. 2004 Feb;25(2):171-6. doi: 10.1016/j.peptides.2003.12.012.
Napins are 1:1 disulfide-linked complexes of a smaller (ca. 4kDa) subunit and a larger (ca. 10kDa) subunit. The intent of the present study was to ascertain the production of napin by the seeds of a Brassica species that has not been examined previously, and also to explore new biological activities of the napin. A heterodimeric 11-kDa napin-like polypeptide has been isolated from Chinese white cabbage (Brassica chinensis cv dwarf) seeds with a protocol comprising ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, fast protein liquid chromatography (FPLC)-ion exchange chromatography on Mono S and FPLC-gel filtration on Superdex 75. The N-terminal sequence of the 7-kDa subunit manifests striking similarity to napin large chain, albumin and trypsin inhibitor. The N-terminal sequence of the 4-kDa subunit is homologous to napin large chain and an antimicrobial peptide. The napin-like polypeptide inhibited translation in the rabbit reticulocyte system with an IC50 of 18.5nM. This translation-inhibitory activity was stable between pH 4 and 11, and between 10 and 40 degrees C. The polypeptide inhibited trypsin with a higher potency ( IC50 = 8.5 microM) than it inhibited chymotrypsin (IC50 = 220 microM), but was devoid of ribonuclease and antifungal activities. It manifested antibacterial activity against Pseudomonas aeruginosia, Bacillus subtilis, Bacillus cereus, and Bacillus megaterium. The results revealed that the napin-like polypeptide from Chinese white cabbage seeds exhibited some potentially exploitable activities.
napin是由一个较小的（约4kDa）亚基和一个较大的（约10kDa）亚基通过1:1二硫键连接形成的复合物。本研究的目的是确定一种此前未被研究过的芸苔属植物种子中napin的产生情况，并探索napin的新生物活性。通过一种包含在DEAE -纤维素上进行离子交换色谱、在Affi -凝胶蓝胶上进行亲和色谱、在Mono S上进行快速蛋白质液相色谱（FPLC）-离子交换色谱以及在Superdex 75上进行FPLC -凝胶过滤的方法，从中国白菜（Brassica chinensis cv dwarf）种子中分离出了一种异源二聚体11kDa的napin样多肽。7kDa亚基的N端序列与napin大链、白蛋白和胰蛋白酶抑制剂具有显著相似性。4kDa亚基的N端序列与napin大链和一种抗菌肽同源。该napin样多肽在兔网织红细胞系统中抑制翻译，IC50为18.5nM。这种翻译抑制活性在pH 4至11以及10至40摄氏度之间稳定。该多肽抑制胰蛋白酶的效力更高（IC50 = 8.5 microM），而抑制糜蛋白酶的效力较低（IC50 = 220 microM），但没有核糖核酸酶和抗真菌活性。它对铜绿假单胞菌、枯草芽孢杆菌、蜡样芽孢杆菌和巨大芽孢杆菌表现出抗菌活性。结果表明，来自中国白菜种子的napin样多肽具有一些潜在的可开发活性。
