Poster: Membrane Transport

Abs # 1207: Glycolipid Modulation of Tonoplast H⁺-ATPase from Cultured Rice (Oryza sativa L. var. Boro) Cells

Presenter:	Yamaguchi, Mineo , yamaguti@rib.okayama-u.ac.jp
Authors	Yamaguchi, Mineo  (A)   Kasamo, Kunihiro  (A)
Affiliations:	(A): Research Institute for Bioresources Okayama University

We extracted phospholipids, glycolipids, acyl steryl glucoside (ASG), and glucocerebroside (GlcCer) from tonoplast fraction of rice. We determined the effects of these lipids on the ATP-hydrolysis activity of tonoplast H⁺-ATPase which was delipidated and purified from the tonoplast fraction. Exogenously-added tonoplast phospholipids stimulated the ATP-hydrolysis activity of purified tonoplast H⁺-ATPase, but tonoplast glycolipids did not. When tonoplast glycolipids or ASG was added in the presence of phospholipids, they decreased the phospholipid-induced activation of the tonoplast H⁺-ATPase; GlcCer only caused a small decrease. Steryl glucoside (SG) did not cause any decrease in this activation. We also reconstituted the tonoplast H⁺-ATPase into the liposome membranes containing ASG or SG. The effects of these glycolipids on H⁺ pumping activity across the proteoliposome membranes were similar to those on ATP-hydrolysis activity. Phospholipids, ASG, and GlcCer comprised 35 mol%, 20 mol% and 7 mol% of the total lipids of the tonoplast fraction of cultured rice cells, respectively, and these glycolipid levels were enough to depress the phospholipid-induced activation of the tonoplast H⁺-ATPase. These results revealed that H⁺-ATPase activity in the tonoplast may be modulated toward activation and depression by tonoplast phospholipids and glycolipids, respectively. The acylation of SG would be responsible for the depression in the phospholipid-induced H⁺-ATPase activity.