ISSN:
1432-2048
Keywords:
Chenopodium
;
Golgi vesicle
;
Proton ATPase
;
Protoplast
;
Sugar nucleotide
;
Suspension cell
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract A microsomal vesicle fraction (GV) markedly enriched by the Golgi marker enzyme latent inosine diphosphatase (IDPase) has been isolated from photoautotrophic suspension-cell protoplasts ofChenopodium rubrum L. Addition of ATP creates a substantial pH gradient across the GV membrane as measured by accumulation of acridine orange. The GV showed a density of 1.14 g·cm-3 by equilibrium density centrifugation on sucrose gradients. Coincidence of acridine-orange accumulation and IDPase activity was confirmed on Percoll gradients. Formation of the pH gradient half-saturates at 0.3 mM MgATP, peaks at pH 7, and is competitively inhibited by ADP (k i≤0.1 mM), but not by Pi; it is hardly inhibited by orthovanadate, quickly dissipated by monensink 2=18 nM), nigericin (k 1/2=25 nM), and sluggishly by N-ethylmaleimide (k 1/2≈35 μM). Inhibition by KNO3 (k 1/2≈6.7 mM) is incomplete (60%). Uridine 5′-diphosphate (UDP)-glucose, UDP-galactose, but not UDP-mannose and the pertinent sugars, dissipate the ATP-generated pH gradient (k 1/2≈10–20 mM UDP-glucose; optimum pH at 7.8). This UDP-glucose activity is accompanied by release of Pi, but not of glucose or sucrose. UDP-glucoseinduced Pi release from the GV saturates (k 1/2=1 mM UDP-glucose; optimum pH at 7) and is completely inhibited by the anion-channel blocker 4,4′-diisothiocyano-2,2′-stilbene disulfonic acid (DIDS;k 1/2=140 μM). The GV incorporates UDP-[U-14C]glucose into an acid-labile, alkaline-stable macromolecular compound; this process is like-wise inhibited by DIDS. We propose a model including, inter alia, a UDP-glucose/uridine-5′-monophosphate translocator and a phosphate-permeable anion channel to operate in Golgi vesicles ofChenopodium rubrum.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00959520
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