Purification and Characterization of Two Sucrose Synthase Isoforms from Japanese Pear Fruit

概要

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Two isoforms(SS I and SS II)of sucrose synthase(SS; EC 2.54.1.13)were purified from Japanese pear fruit and their properties were compared. SS I mainly appeared in young fruit and SS II mainly in mature fruit. SS I and SS II were purified to the specific activity of 3.37 and 4.26(units(mg protein)^<-1>), respectively. The MW of native and subunit proteins of SS I and SS II were almost the same and both SSs seemed to be a tetramer composed of an 83 kDa polypeptide. However, the ionic charges of the native proteins and the kinetic parameters of SSs were different. Specifically, the K_m value for UDP-glucose in SS I was the same as that for UDP, while the K_m value for UDP-glucose in SS II was less than that for UDP. SS II easily reacted for sucrose synthesis than sucrose cleavage compared with SS I. Therefore, it is considered that SS I and SS II play different roles in the utilization of carbohydrate in young and mature fruit, respectively.
日本植物生理学会の論文