Zhang X Q, Chollet R
Department of Biochemistry, University of Nebraska-Lincoln, George W. Beadle Center, 68588-0664, USA.
FEBS Lett. 1997 Jun 30;410(2-3):126-30. doi: 10.1016/s0014-5793(97)00537-1.
Sucrose synthase (SS; EC 2.4.1.13) was radiolabeled in situ by incubating detached soybean nodules with 32Pi. Phosphoamino acid analysis indicated that SS was phosphorylated on a serine residue(s). In-vitro phosphorylation of purified nodule SS by desalted nodule extracts was Ca2+-dependent. This SS-kinase was partially purified (approximately 2200-fold) from nodules harvested from illuminated plants. The molecular mass of the SS-kinase was about 55,000 on a Superdex 75 size-exclusion column or in a denaturing autophosphorylation gel. With either purified nodule SS or Syntide 2 as substrate, exogenous calmodulin and phosphatidylserine showed little or no effect on the in-vitro activity of this partially purified protein kinase. However, its activity was inhibited by W-7. The purified nodule SS-kinase (or CDPK) phosphorylated nodule PEP carboxylase (PEPC; EC 4.1.1.31) in the presence of Ca2+. In contrast, a partially purified nodule PEPC-kinase preparation was incapable of phosphorylating nodule SS. Unlike nodule PEPC [Zhang et al. (1995) Plant Physiol. 108, 1561-1568], the phosphorylation state of SS is not likely modulated in planta by photosynthate supply from the shoots.
通过用³²Pᵢ孵育离体大豆根瘤，对蔗糖合酶（SS；EC 2.4.1.13）进行原位放射性标记。磷酸氨基酸分析表明，SS在一个丝氨酸残基上发生了磷酸化。用脱盐的根瘤提取物对纯化的根瘤SS进行体外磷酸化是Ca²⁺依赖性的。这种SS激酶是从光照下生长的植株收获的根瘤中部分纯化得到的（约2200倍）。在Superdex 75尺寸排阻柱上或变性自磷酸化凝胶中，SS激酶的分子量约为55,000。以纯化的根瘤SS或合成肽2为底物时，外源钙调蛋白和磷脂酰丝氨酸对这种部分纯化的蛋白激酶的体外活性几乎没有影响。然而，其活性受到W - 7的抑制。在Ca²⁺存在的情况下，纯化的根瘤SS激酶（或钙依赖蛋白激酶）使根瘤磷酸烯醇式丙酮酸羧化酶（PEPC；EC 4.1.1.31）发生磷酸化。相反，部分纯化的根瘤PEPC激酶制剂不能使根瘤SS发生磷酸化。与根瘤PEPC不同[Zhang等人（1995年）《植物生理学》108卷，1561 - 1568页]，SS的磷酸化状态在植物体内不太可能受来自地上部光合产物供应的调节。
