The role of auxin-binding protein during growth and development of fruit

苹果幼苗生长素结合蛋白经2，4-D连接琼脂糖4B亲和层析和2次Sepharose4B凝胶过滤后得到部分纯化。经SDS-PAGE分析，其分子量约为400 KDa，由56 KDa和15 KDa的亚基组成，其大小与6种结合活性的强弱成正比。用Scatchard作图法测得解离常数为7.7×10~(-6)M。该结合蛋白与绿豆幼苗中的ABP-I相似。其结合活性可被2，4-D和NAA完全抑制，被抗生长素的PCIB抑制约50%。用相同方法部分纯化的甜瓜幼苗生长素结合蛋白显示，硫酸铵沉淀法和平衡透析法测定的生长素结合蛋白活性相当。该蛋白的相对分子质量为155 KDa，解离常数为4.8×10~(-6)~(-6)M，可与1个以上的IAA结合。梅隆幼苗中的生长素结合蛋白类似于绿豆种子中的ABP-II，目前还没有对两种生长素结合蛋白的功能进行详细的研究。然而，我们可以坚定地认为，这些生长素结合蛋白具有生长素受体的特征，这是由底物的特异性、反应对底物浓度的饱和度和反应的可逆性来定义的。

Auxin-binding protein in apple seedling was partially purified by 2, 4-D linked-Sephasrose 4B affinity chromatography and 2 times of Sepharose 4B gel filtration. It had a molecular weight of about 400 KDa and was composed of subunit bands of 56 KDa ana 15 KDa by SDS-PAGE, which appeared in proportion to the strength of 6binding activity. The dissociation constant by Scatchard plot was 7.7X1O^<-6> M. This binding protT4n is similar to ABP-I from mung bean seedling. The binding activity to ^<14>C-IAA was completely inhibited by 2, 4-D and NAA, and inhibited to about 50% by PCIB of antiauxin. Auxin-binding protein in melon seedling partially purified by the same procedure showed the equal activity between both assay methods of an ammonium sulfate precipitation and an equilibrating dialysis. The protein had a molecular weight of 155 KDa and a dissociation constant of 4.8X1O^<-6> M, and combined more than one molar IAA to one molar protein. This binding protein from mellon seedling is like ABP-II from mung bean seedling.The function about two kinds of the auxin-binding protein was not investigated in detail through the present experiment. However, we can suggest firmly these auxin binding proteins possess the characteristics as an auxin receptor, as defined by the specificity for substrate, the saturation of reaction to substrate concentration and the reversibility of reaction.