Evidence for a uridine-5'-diphosphate-glucose-protectedp-chloromercuribenzene sulfonic acid-binding site in sugarcane vacuoles.

The uptake of uridine-5'-diphosphate (UDP) glucose into vacuoles isolated fromSaccharum sp. cells was fully inhibited by pretreatment with 50 μMp-chloromercuribenzenesulfonic acid (PCMBS) and was not affected by N-ethylmaleimide up to a concentration of 5 mM. The addition of 10 mM UDP-glucose during the pretreatment partially protected the uptake mechanism from PCMBS inhibition, while the presence of adenosine-5'-diphosphate (ADP) glucose or of various hexose-phosphates had no protective effect. Parallel experiments on the binding of [(203)Hg]PCMBS to the vacuoles showed that UDP-glucose and UDP added at 10 mM concentrations caused a 40% decrease in the binding of PCMBS while ADP-glucose did not inhibit the binding. The results indicate the presence in a previously proposed group translocator of at least one site that can bind UDP-glucose. This site, which is blocked by PCMBS, interacts with the nucleotide moiety of UDP-glucose.