Sun S S, Altenbach S B, Leung F W
Eur J Biochem. 1987 Feb 2;162(3):477-83. doi: 10.1111/j.1432-1033.1987.tb10665.x.
An abundant seed protein, which is exceptionally rich in the sulfur-containing amino acids, methionine (18%) and cysteine (8%), is synthesized in Brazil nut embryos about 9 months after flowering. This sulfur-rich protein consists of two low-molecular-mass polypeptide components, a 9-kDa polypeptide and a 3-kDa polypeptide. The two-subunit polypeptides associate through disulfide linkage(s) to form a 12-kDa protein molecule. We have demonstrated through in vitro translation studies, using RNA from 9-month-old embryos, that the sulfur-rich protein is synthesized as a larger precursor polypeptide of 18 kDa. In addition, data from in vivo labelling studies of 9-month-old Brazil nuts suggest that there are two intermediate precursors of the sulfur-rich protein, one of 15 kDa and another of 12 kDa. One of these precursors, the 12-kDa polypeptide, accumulates for a 2-month period in the developing embryos. From these data we infer that at least three stepwise cleavages are involved in the maturation of the sulfur-rich protein from its 18-kDa precursor.
一种富含种子的蛋白质在巴西坚果开花后约9个月的胚胎中合成，这种蛋白质特别富含含硫氨基酸甲硫氨酸（18%）和半胱氨酸（8%）。这种富含硫的蛋白质由两个低分子量多肽组分组成，一个9 kDa的多肽和一个3 kDa的多肽。这两个亚基多肽通过二硫键结合形成一个12 kDa的蛋白质分子。我们通过使用9个月大胚胎的RNA进行体外翻译研究证明，富含硫的蛋白质是以18 kDa的较大前体多肽形式合成的。此外，对9个月大巴西坚果的体内标记研究数据表明，富含硫的蛋白质有两个中间前体，一个15 kDa，另一个12 kDa。这些前体之一，即12 kDa的多肽，在发育中的胚胎中积累2个月。从这些数据我们推断，富含硫的蛋白质从其18 kDa前体成熟至少涉及三个逐步切割步骤。
