Sodium‐dependent Transport of [³H](1d)chiro‐Inositol by Tetrahymena

Abstract

The transport characteristics of (1D)chiro-inositol by the ciliate Tetrahymena were examined in competition studies employing [3H](1D)chiro-inositol. (1D)chiro-Inositol transport was competed by unlabeled (1D)chiro-inositol, myo-inositol, scyllo-inositol, and D-glucose in a concentration-dependent manner. Conversely, (1D)chiro-inositol competed for [3H]myo- and [3H]scyllo-inositol transport. Lineweaver-Burke analysis of the competition data indicated a Km of 10.3 mM and a Bmax of 4.7 nmol/min/mg for (1D)chiro-inositol. Transport of (1D)chiro-inositol was inhibited by cytochalasin B, an inhibitor of facilitated glucose transporters, and phlorizin, an inhibitor of sodium-dependent transporters. Removal of sodium from the radiolabeling buffer also inhibited uptake. The presence of 0.64 mM calcium or magnesium ions exerted negligible effects on transport, although potassium was inhibitory. [3H](1D)chiro-Inositol was shown to be incorporated into Tetrahymena phosphoinositides.

Arabidopsis INOSITOL TRANSPORTER2 Mediates H+ Symport of Different Inositol Epimers and Derivatives across the Plasma Membrane

“…For the ciliate Tetrahymena vorax, for example, it was found that the most frequently occurring epimers myo-, scyllo-, and D-chiroinositol were transported across the plasma membrane (Kersting and Ryals, 2004). Similarly, it was shown for human HepG2 liver cells that myoinositol and D-chiroinositol are transported by the same protein (Ostlund et al, 1996).…”

Phosphatidylinositol Synthase of Tetrahymena: Inositol Isomers as Substrates in Phosphatidylinositol Biosynthesis and Headgroup Exchange Reactions

“…Phosphatidylinositol that contains a scyllo ‐ or chiro ‐Ins headgroup rather than a myo ‐Ins headgroup has been reported (Carstensen et al 1999; Futerman et al 1985; Kersting and Ryals 2004; Mato et al 1987; Ryals and Kersting 1999). Our results indicate that each inositol isomer tested can serve as substrate for T. vorax PtdIns synthase in vitro with the order of substrate preference being myo ‐Ins> scyllo ‐Ins>(1 d ) chiro ‐Ins> epi ‐Ins>(1 l ) chiro ‐Ins> allo ‐Ins> muco ‐Ins.…”

“…To our knowledge no data are available on the comparative kinetics. Previous work has shown that Tetrahymena transport myo-, scyllo-, and (1D)chiro-Ins by a sodium-dependent mechanism and that each of these inositol isomers is utilized to form the corresponding PtdIns (Kersting and Ryals 2004;Kersting et al 2003;Ryals and Kersting 1999).…”

“…Phosphatidyl‐ scyllo ‐inositol is present in barley seed (Carstensen et al 1999; Kinnard et al 1995; Murthy et al 1992; Narasimhan et al 1997). Other studies have shown that Tetrahymena contain isomeric PtdIns derived from scyllo‐ , chiro ‐, and neo ‐Ins (Kersting et al 2003; Kersting and Ryals 2004; Ryals and Kersting 1999). …”

Conservation and Innovation in Tetrahymena Membrane Traffic: Proteins, Lipids, and Compartments

“…Inositol exists as a number of stereoisomers, the most common of which is myo-inositol, but other isomers are also present in cells including scyllo -, neo -, epi-D-chiro - and muco-inositols. In T. vorax , non- myo -inositols have also been detected, with evidence that these can be taken up from the medium(Kersting et al, 2003; Kersting and Ryals, 2004; Ryals and Kersting, 1999). Conversion between inositol isomers may also occur via inositol epimerases(Sun et al, 2002), though no conclusive genetic or biochemical data have been published in Tetrahymena to date.…”