MIMOSA PUDICA APYRASE REQUIRES POLYSACCHARIDE AND CA2+ FOR THE ACTIVITY

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 suga rs. The apparent molecular mass of these 2 isoforms are 36 and 34 Kd r espectively. The association of the polysaccharide with the isoform I has been found to be Ca2+ dependent which is endogenously present in t his isoform. Removal of Ca2+ and polysaccharide from the enzyme (isofo rm I) leads to an inactivation. The enzyme activity can be restored wh en both Ca2+ and endogenous polysaccharide fraction were added at an o ptimal molar ratio of Ca2+:protein of 7:1. The endogenous polysacchari de can be replaced by the standard arabinogalactan. No other sugar or polysaccharide except the arabinogalactan can restore the apyrase acti vity. Calcium mediates a conformational change in the protein which he lps in association of polysaccharide as evidenced from fluorometric an d far UV-CD studies to restore the enzymic activity. Neither any inter action of the polysaccharide with the protein is detected in absence o f Ca2+ nor the enzyme activity could be recovered under such condition .