Purification and characterization of sucrose synthase isozymes from etiolated rice seedlings

Presence of homo- and hetero-tetrameric rice sucrose synthase (RSS) isoforms in etiolated rice seedlings was demonstrated by immunoprecipitation using monospecific antibodies. Three RSS isozymes with various pI values were purified by ammonium sulfate fractionation, Sepharose CL-6B gel filtration, DEAE-Sephacel and Mono-Q ion exchange chromatographies. They were characterized as heterotetramers composed of RSS1 and RSS2 subunits. All of them used UDP as the best substrate. The presence of divalent metal ions increased the activities of synthesis but inhibited the cleavage of sucrose.