Ghosh R, Sen P C, Biswas S
Department of Biochemistry, Bose Institute, Calcutta, India.
Mol Cell Biochem. 1998 Oct;187(1-2):47-55. doi: 10.1023/a:1006855627784.
Mimosa pudica Linn leaves with pulvini contain unique isoforms (I and II) of Apyrase enzyme (EC 3.6.1.5). The activity of isoform I depends on divalent cation Mn2+. This isoform is associated noncovalently with the polysaccharide, containing mainly of galactose and arabinose sugars. The apparent molecular mass of these 2 isoforms are 36 and 34 Kd respectively. The association of the polysaccharide with the isoform I has been found to be Ca2+ dependent which is endogenously present in this isoform. Removal of Ca2+ and polysaccharide from the enzyme (isoform I) leads to an inactivation. The enzyme activity can be restored when both Ca2+ and endogenous polysaccharide fraction were added at an optimal molar ratio of Ca2+:protein of 7:1. The endogenous polysaccharide can be replaced by the standard arabinogalactan. No other sugar or polysaccharide except the arabinogalactan can restore the apyrase activity. Calcium mediates a conformational change in the protein which helps in association of polysaccharide as evidenced from fluorometric and far UV-CD studies to restore the enzymic activity. Neither any interaction of the polysaccharide with the protein is detected in absence of Ca2+ nor the enzyme activity could be recovered under such condition.
含羞草具叶枕的叶子含有独特的ATP双磷酸酶（EC 3.6.1.5）同工型（I和II）。同工型I的活性取决于二价阳离子Mn2+。该同工型与主要含有半乳糖和阿拉伯糖的多糖非共价结合。这两种同工型的表观分子量分别为36和34 kDa。已发现多糖与同工型I的结合是Ca2+依赖性的，Ca2+内源性存在于该同工型中。从酶（同工型I）中去除Ca2+和多糖会导致失活。当以Ca2+与蛋白质7:1的最佳摩尔比添加Ca2+和内源性多糖组分时，酶活性可以恢复。内源性多糖可以被标准阿拉伯半乳聚糖替代。除阿拉伯半乳聚糖外，没有其他糖或多糖能恢复ATP双磷酸酶活性。荧光和远紫外圆二色性研究表明，钙介导蛋白质的构象变化，这有助于多糖的结合以恢复酶活性。在没有Ca2+的情况下，未检测到多糖与蛋白质的任何相互作用，在此条件下也无法恢复酶活性。
