OCCURRENCE OF 2 SUCROSE SYNTHASE ISOZYMES DURING MATURATION OF JAPANESE PEAR FRUIT

The properties of sucrose synthase (SS) isozymes partially purified fr om immature fruit (SS II) of Japanese pear (Pyrus serotina Rehder var, culta Rehder) were different than those of mature fruit (SS II), A cl ear difference in elusion pattern during DEAE-cellulose chromatography was observed, although the apparent molecular weight of the native pr oteins extracted from both stages was 350 kD, The Km value of SS II fo r UDP was similar to that for UDP-glucose; while with SS I, the Km for UDP was lower than that for UDP-glucose. This suggests that SS II act ivity favors sucrose synthesis compared with SS I, which favors sucros e cleavage. The optimum pH for activity toward sucrose synthesis was 8 .0 for SS II and 8.5 to 9.5 for SS I, SS II from mature fruit may be a n isozyme of SS occurring during periods of rapid sucrose accumulation , while SS I from immature fruit is more similar to the typical SS whi ch functions mainly toward sucrose cleavage in many plants.