Effects of Lens Major Intrinsic Protein on Glycerol Permeability and Metabolism |
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Authors: | C Kushmerick K Varadaraj RT Mathias |
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Institution: | (1) Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York 11794-8661, USA, US |
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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).
Received: 23 May 1997/Revised: 4 August 1997 |
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Keywords: | : 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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