Preliminary Evidence for Solubilization of an Active Tonoplast-Bound Vectorial Sucrose Synthesizing Enzyme Complex
The existence of a UDP-glucose-dependent vectorial mechanism for the formation of vacuolar sucrose on the tonoplast has been demonstrated on a number of different plant species (Thom and Maretzki, 1985; Thom et al., 1986; Oleski et al., 1986). The evidence, so far, indicates that hexose phosphates cannot penetrate the tonoplast membrane any better than can free hexoses, sucrose, or sucrose-P (Thom and Maretzki, 1985; Maretzki and Thom, 1986). This implies that the appearance of labeled sucrose-P and free sucrose inside vacuoles from the external addition of UDPG-glucose labeled in the glucose moiety requires the formation of fructose-6 P from the added UDP-glucose. Indeed, this hypothesis is further strengthened by the fact that neither cold UDP-glucose added simultaneously with labeled fructose-6 P, nor UDP-glucose, labeled in the nucleotide moiety lead to the appearance of label associated with the vacuole (Thom and Maretzki, 1986).
KeywordsPellet Fraction Detergent Concentration Protoplast Suspension Hexose Phosphate Tonoplast Vesicle
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