Abstract: A sweet protein, brazzein, has been discovered from the fruits of Pentadiplandra brazzeana B., a tropical wild plant in west Africa. Brazzein has 54 amino acid residues; it is 2000 times sweeter than sucrose (Ming and Hellekant, 1994 ). In this article, further characterization shows that its molecular weight is 6.5 kD and isoelectric point is 5. It has 8 cysteines and they form four disulfide bonds. After treating its aqueous solution at 80 ℃ for 4 hrs, no changes in sweetness and behavior of electrophoresis are found. Secondary structures predictions suggests that beta turns and beta sheets are the dominant structures in the protein.

Key words: Pentadiplandra brazzeana, Sweet protein brazzein, Chemicl modification

摘要： Ming and Hellekant（1994）从西非洲热带野生植物 Pentadiplandra brazzeana Baill．的果实中，分离出一种甜味蛋白质，命名为brazzein，它是由54个氨基酸残基组成的单链多肽；甜度是蔗糖的2000倍。本实验测得 Brazzein分子量为 6.5 kD，等电点为 5。Brazzein含有 8个半胱氨酸，构成分子内的双硫键；其水溶液经 80℃，4 h处理，甜味和电泳行为不变。虽然 Brazzein的氨基酸序列与芥菜蛋白酶抑制剂MTI—2有高的同源性，但未测出有蛋白酶抑制剂活性。根据氨基酸序列的计算机分析表明：Brazzein是亲水性多肽；二级结构主要是β-折途和β-转角。蛋白质印迹分析显示，Brazzein抗血清与甜味蛋白curculin，mabinlin和miraculin有强的交叉反应。Brazzein的S-基化修饰引起甜味的丧失，同时也丧失与抗血清的免疫反应。Brazzein中赖氨酸ε-氨基的酰化，酪氨酸酚羟基的碘化，组氨酸咪唑基和精氨酸胍基的修饰均导致甜味的丧失或降低；但赖氨酸ε-氨基的甲基化只改变其电泳行为，却不降低甜味。这表明Brazzein分子的表面电荷对于其甜味性质是重要的。

关键词: pentadiplandra brazzeana, 甜味蛋白质, 化学修饰