葡萄果实中脱落酸结合蛋白的存在及其性质

葡萄果实微粒体上存在高亲和力的脱落酸（ＡＢＡ）结合位点，这些位点与ＡＢＡ的结合具有饱和性，高亲和力及低容量，胰蛋白酶或ＤＴＴ处理可以使该位点的特异结合活性下降约９０％，表明此结合位点是一种蛋白质，故称为ＡＢＡ结合蛋白，它含有维系蛋白质特定构象的二硫键，该蛋白与ＡＢＡ反应的最适ｐＨ为６．０，说明与配基结合部位可能存在带有正电荷的氨基酸残基，结合活性在２５℃高于０℃，结合反应达到动态平衡需要３０ｍｉｎ，３０ｍｉｎ以后结合活性随时间延长而下降。该蛋白与ＡＢＡ结合反应的平衡解离常数为１７．５ｎｍｏｌ／Ｌ，最大结合容量（Ｂｍａｘ）为９８．４ｆｍｏｌ／ｍｇｐｒｏｔｅｉｎ。

The Abscisic Acid Binding Proteins and Their Properties in Grapevine Fruits

Abscisic acid(ABA) plays a key role in the regulation of grapevine fruit ripening,but the cellular and molecular biological mechanism of the hormone action in the fruit ripening remains unknown.By means of differential centrifugation,microsomes were prepared from Kyoho grapevine(Vitis vinifera L.×V.labrusca L.) berries,and by using the microsomes,evidence for the occurence of specific ABA-binding sites on the membranes have been obtained with the microvolume radioactivity ligand binding assay.The binding sites possessed the properties of saturability,high affinity and low capacity.The results of trypsin and dithiothreitol treatments to the microsomes suggested that ABA binding sites showed the properties of proteins and there might be disulfide group located at or near the binding site.The maximum binding amount of ABA in the microsomes was at pH6.0 and the activity of ABA binding proteins was higher at 25℃than at 0℃.The amount of ABA bound reached 54% of the ABA maximum binding(Bmax) after incubation for 10 min and reached to Bmax after incubation for 30 mins.The dissociation constant(Ka) and Bmax of ABA binding proteins in the microsomes were 17.5 nmol/L and 98.4 fmol/mg protein respectively.