Inquello V, Raymond J, Azanza J L
Institut des Sciences et Techniques des Aliments de Bordeaux, Université Bordeaux I, Talence, France.
Eur J Biochem. 1993 Nov 1;217(3):891-5. doi: 10.1111/j.1432-1033.1993.tb18318.x.
Cruciferin, the main storage protein in rapeseed (Brassica napus L.), is a legumin-like 11S globulin. Using SDS/PAGE cruciferin was shown to be composed of different subunits consisting of alpha S and beta S polypeptides, which were disulfide linked, and also closely related free alpha f and beta f polypeptides which were not covalently linked. The origin of these latter free chains was found to be the result of disulfide interchange reactions occurring during SDS-induced dissociation of the hexameric 11S complex. These reactions involved the rupture of the alpha S-beta S interchain disulfide link and, as shown by specific thiol fluorescent labeling, the subsequent formation of an intra-beta-chain disulfide bond. N-terminal amino acid sequence determinations revealed that these reactions were related to particular cruciferin subunit beta chains having an additional cysteine residue (position 11) near the residue (position 7) implicated in the inter-chain disulfide bridges. Such a sequence could explain the origin of the free and linked polypeptides as also shown in SDS/PAGE analysis of radish (Raphanus sativum L.) and Arabidopsis thaliana H. cruciferins. These two polypeptide classes may be considered to represent phenotypic biochemical markers of two different Cruciferae globulin gene families.
十字花科球蛋白是油菜籽（甘蓝型油菜）中的主要贮藏蛋白，是一种豆球蛋白样的11S球蛋白。通过SDS/PAGE分析表明，十字花科球蛋白由不同的亚基组成，这些亚基由αS和βS多肽组成，它们通过二硫键相连，还有与之密切相关的游离αf和βf多肽，它们没有共价连接。发现这些游离链的来源是六聚体11S复合物在SDS诱导解离过程中发生的二硫键交换反应的结果。这些反应涉及αS-βS链间二硫键的断裂，并且如特定硫醇荧光标记所示，随后形成链内β链二硫键。N端氨基酸序列测定表明，这些反应与特定的十字花科球蛋白亚基β链有关，这些β链在参与链间二硫键桥的残基（位置7）附近有一个额外的半胱氨酸残基（位置11）。这样的序列可以解释游离和连接多肽的来源，这也在萝卜（萝卜）和拟南芥十字花科球蛋白的SDS/PAGE分析中得到了体现。这两类多肽可被视为两个不同十字花科球蛋白基因家族的表型生化标记。
