Preliminary Evidence for Solubilization of an Active Tonoplast-Bound Vectorial Sucrose Synthesizing Enzyme Complex

Abstract

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).

Published as Paper No. 616 in the Journal Series of the Experiment Station, Hawaiian Sugar Planters’ Association.