Purification and characterization of two sucrose synthase isoforms from Japanese pear fruit.
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 Km value for UDP-glucose in SS I was the same as that for UDP, while the Km 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.
Tanase
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Laboratory of Horticultural Science, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Japan.
Yamaki
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S
D005638:Fruit / Q000201:enzymology*; D005964:Glucosyltransferases / Q000302:isolation & purification*; D020033:Protein Isoforms / Q000302:isolation & purification; D019685:Rosales / Q000201:enzymology*
D020033:Protein Isoforms; D005964:Glucosyltransferases; C022699:sucrose synthase