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The Journal of Membrane Biology

, Volume 161, Issue 1, pp 9–19 | Cite as

Effects of Lens Major Intrinsic Protein on Glycerol Permeability and Metabolism

  • C.  Kushmerick
  • K.  Varadaraj
  • R.T.  Mathias

Abstract.

Lens Major Intrinsic Protein (MIP) is a member of a family of membrane transport proteins including the Aquaporins and bacterial glycerol transporters. When expressed in Xenopus oocytes, MIP increased both glycerol permeability and the activity of glycerol kinase. Glycerol permeability (p Gly ) was 2.3 ± 0.23 × 10−6 cm sec−1 with MIP vs. 0.92 ± 0.086 × 10−6 cm sec−1 in control oocytes. The p Gly of MIP was independent of concentration from 5 × 10−5 to 5 × 10−2 m, had a low temperature dependence, and was inhibited approximately 90%, 80% and 50% by 1.0 mm Hg++, 0.2 mm DIDS (diisothiocyanodisulfonic stilbene), and 0.1 mm Cu++, respectively. MIP-enhanced glycerol phosphorylation, resulting in increased incorporation of glycerol into lipids. This could arise from an increase in the total activity of glycerol kinase, or from an increase in its affinity for glycerol. Based on methods we present to distinguish these mechanisms, MIP increased the maximum rate of phosphorylation by glycerol kinase (0.12 ± 0.03 vs. 0.06 ± 0.01 pmol min−1 cell−1) without changing the binding of glycerol to the kinase (K M ∼ 10 μm).

Key words: MIP26 — Lens fiber cell — Glycerol — Cell membrane permeability — Glycerol kinase Abbreviations: DIDS, diisothiocyanodisulfonic stilbene; G3P, α-glycerol-3-phosphate; GK, Glycerol Kinase EC 2.7.1.30; MIP, Major Intrinsic Protein of Lens 

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Copyright information

© Springer-Verlag New York Inc. 1998

Authors and Affiliations

  • C.  Kushmerick
    • 1
  • K.  Varadaraj
    • 1
  • R.T.  Mathias
    • 1
  1. 1.Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York 11794-8661, USAUS

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