Insulin does not induce the hydrolysis of a glycosyl phosphatidylinositol in rat fetal hepatocytes

The molecular events involved in the cellular actions of insulin remain unexplained. Some of the acute actions of the hormone may be due to the intracellular generation of a chemical substance which modulates certain enzyme activities. Such an enzymemodulating substance has been identified as an inositol phosphate-glycan, produced by the insulin-sensitive hydrolysis of a glycosyl-phosphatidylinositol (glycosyl-Ptdlns) precursor. This precursor glycolipid is structurally similar to the glycosylphosphoinositide membrane protein anchor. The exposure of fat, liver or muscle cells to insulin results in the hydrolysis of glycosyl-Ptdlns, giving rise to the inositol phosphate glycan and diacylglycerol. This hydrolysis reaction is catalysed by a glycosyl-PtdIns-specific phospholipase C. This enzyme has been characterized and purified from a plasma membrane fraction of liver. This reaction also results in the acute release of certain glycosyl-Ptdlns-anchored proteins from the cell surface. Elucidation of the functional role of glycosyl-phosphoinositides in the generation of second messengers or the release of proteins may provide further insights into the pleiotropic nature of insulin action.

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Ectoenzymes of the kidney microvillar membrane. Isolation and characterization of the amphipathic form of renal dipeptidase and hydrolysis of its glycosyl-phosphatidylinositol anchor by an activity in plasma

Biochemical Journal ◽

10.1042/bj2610811 ◽

1989 ◽

Vol 261 (3) ◽

pp. 811-818 ◽

Cited By ~ 20

Author(s):

N M Hooper ◽

A J Turner

Keyword(s):

Membrane Anchor ◽

Glycosyl Phosphatidylinositol ◽

Isolation And Characterization ◽

C Terminus ◽

Terminal Amino ◽

Membrane Isolation ◽

Solubilized Form ◽

Triton X ◽

Hydrolysis Of

Renal dipeptidase (EC 3.4.13.11) has been solubilized from pig kidney microvillar membranes with n-octyl-beta-D-glucopyranoside and then purified by affinity chromatography on cilastatin-Sepharose. The enzyme exists as a disulphide-linked dimer of two identical subunits of Mr 45,000 each. The purified dipeptidase partitioned into the detergent-rich phase upon phase separation in Triton X-114 and reconstituted into liposomes consistent with the presence of the glycosyl-phosphatidylinositol membrane anchor. The N-terminal amino acid sequence of the amphipathic, detergent-solubilized, form of renal dipeptidase was identical with that of the hydrophilic, phospholipase-solubilized, form, locating the membrane anchor at the C-terminus of the protein. The glycosyl-phosphatidylinositol anchor of both purified and microvillar membrane renal dipeptidase was a substrate for an activity in pig plasma which displayed properties similar to those of a previously described phospholipase D. The cross-reacting determinant of the glycosyl-phosphatidylinositol anchor was generated by incubation of purified renal dipeptidase with bacterial phosphatidylinositol-specific phospholipase c, whereas the anchor-degrading activity in plasma failed to generate this determinant.

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An Explanation for the Adiponectin Paradox

Pharmaceuticals ◽

10.3390/ph14121266 ◽

2021 ◽

Vol 14 (12) ◽

pp. 1266

Author(s):

Hans O. Kalkman

Keyword(s):

Insulin Resistance ◽

Signal Transduction ◽

Insulin Sensitivity ◽

Phospholipase D ◽

Functional Consequence ◽

Glycosyl Phosphatidylinositol ◽

Paradoxical Situation ◽

Hydrolysis Of ◽

Circulating Levels ◽

Sensitivity Functional

The adipokine adiponectin improves insulin sensitivity. Functional signal transduction of adiponectin requires at least one of the receptors AdipoR1 or AdipoR2, but additionally the glycosyl phosphatidylinositol-anchored molecule, T-cadherin. Overnutrition causes a reduction in adiponectin synthesis and an increase in the circulating levels of the enzyme glycosyl phosphatidylinositol-phospholipase D (GPI-PLD). GPI-PLD promotes the hydrolysis of T-cadherin. The functional consequence of T-cadherin hydrolysis is a reduction in adiponectin sequestration by responsive tissues, an augmentation of adiponectin levels in circulation and a (further) reduction in signal transduction. This process creates the paradoxical situation that adiponectin levels are augmented, whereas the adiponectin signal transduction and insulin sensitivity remain strongly impaired. Although both hypoadiponectinemia and hyperadiponectinemia reflect a situation of insulin resistance, the treatments are likely to be different.

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Lipid metabolism in Trypanosoma brucei: utilization of myristate and myristoyllysophosphatidylcholine for myristoylation of glycosyl phosphatidylinositols

Biochemical Journal ◽

10.1042/bj3180575 ◽

1996 ◽

Vol 318 (2) ◽

pp. 575-581 ◽

Cited By ~ 14

Author(s):

Karl A WERBOVETZ ◽

Paul T ENGLUND

Keyword(s):

Fatty Acid ◽

Trypanosoma Brucei ◽

Surface Glycoprotein ◽

Free System ◽

Glycosyl Phosphatidylinositol ◽

Physiological Importance ◽

Fatty Acid Species ◽

Rapid Hydrolysis ◽

Hydrolysis Of

Myristate is the exclusive fatty acid species in the glycosyl phosphatidylinositol (GPI) anchor of the Trypanosoma brucei variant surface glycoprotein (VSG). [3H]Myristate can be incorporated into T. brucei GPIs by two distinct processes known as fatty acid remodelling and myristate exchange. Myristoyllysophosphatidylcholine (M-LPC) can also serve as a myristate donor for VSG in trypanosomes [Bowes, Samad, Jiang, Weaver and Mellors (1993) J. Biol. Chem. 268, 13885–13892]. We have studied in detail the myristoylation of GPIs using a [3H]M-LPC substrate. Labelling of VSG and free GPIs by [3H]M-LPC in cultured trypanosomes occurred at the same rate as with [3H]myristate. Concurrent with GPI labelling, there was rapid hydrolysis of [3H]M-LPC to generate extracellular [3H]myristate. Experiments in a trypanosomal cell-free system indicated that GPI labelling by fatty acid remodelling and myristate exchange was also equally efficient with [3H]M-LPC and [3H]myristate. Furthermore, both ATP and CoA are required for the myristoylation of GPIs by [3H]M-LPC. These experiments suggest that GPI myristoylation from M-LPC involves hydrolysis of M-LPC to free myristate. To address the physiological importance of myristate and M-LPC in VSG myristoylation, we radiolabelled trypanosomes in vivo with both substrates in medium containing serum, and found that [3H]myristate labelled VSG and GPIs more efficiently. Thus, VSG myristoylation by free myristate may be favoured in bloodstream trypanosome infections.

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Hydrolysis of Glycosyl-Phosphatidylinositol in Response to Insulin is Reduced in Cells Bearing Kinase-Deficient Insulin Receptors

Growth Factors ◽

10.3109/08977199009071496 ◽

1990 ◽

Vol 2 (2) ◽

pp. 91-97 ◽

Cited By ~ 18

Author(s):

Mayte Villalba ◽

Jose F. Alvarez ◽

David S. Russell ◽

Jose M. Mato ◽

Ora M. Rosen

Keyword(s):

Insulin Receptors ◽

Glycosyl Phosphatidylinositol ◽

Hydrolysis Of ◽

In Cells

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Hydrolysis of the glycosyl-phosphatidylinositol anchors of renal microvillar peptidases by a plasma phospholipase D

Biochemical Society Transactions ◽

10.1042/bst0170885 ◽

1989 ◽

Vol 17 (5) ◽

pp. 885-886 ◽

Cited By ~ 6

Author(s):

NIGEL M. HOOPER ◽

ANTHONY J. TURNER

Keyword(s):

Phospholipase D ◽

Glycosyl Phosphatidylinositol ◽

Hydrolysis Of

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Fine Structural Localization of Acyltransferases Involved in Lipid Synthesis in Intestinal Mucosa.

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100067261 ◽

1970 ◽

Vol 28 ◽

pp. 54-55

Author(s):

R. J. Barrnett ◽

J. A. Higgins

Keyword(s):

Smooth Endoplasmic Reticulum ◽

Lipid Synthesis ◽

Mucosal Cell ◽

Structural Localization ◽

Morphological Studies ◽

Mucosal Cells ◽

Initial Appearance ◽

Sh Group ◽

Hydrolysis Of ◽

Intestinal Mucosal Cells

The main products of intestinal hydrolysis of dietary triglycerides are free fatty acids and monoglycerides. These form micelles from which the lipids are absorbed across the mucosal cell brush border. Biochemical studies have indicated that intestinal mucosal cells possess a triglyceride synthesising system, which uses monoglyceride directly as an acylacceptor as well as the system found in other tissues in which alphaglycerophosphate is the acylacceptor. The former pathway is used preferentially for the resynthesis of triglyceride from absorbed lipid, while the latter is used mainly for phospholipid synthesis. Both lipids are incorporated into chylomicrons. Morphological studies have shown that during fat absorption there is an initial appearance of fat droplets within the cisternae of the smooth endoplasmic reticulum and that these subsequently accumulate in the golgi elements from which they are released at the lateral borders of the cell as chylomicrons.We have recently developed several methods for the fine structural localization of acyltransferases dependent on the precipitation, in an electron dense form, of CoA released during the transfer of the acyl group to an acceptor, and have now applied these methods to a study of the fine structural localization of the enzymes involved in chylomicron lipid biosynthesis. These methods are based on the reduction of ferricyanide ions by the free SH group of CoA.

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Lattice imaging and pore structure of β ferric oxyhydroxide

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108465 ◽

1978 ◽

Vol 36 (1) ◽

pp. 264-265

Author(s):

T. Baird ◽

J.R. Fryer ◽

S.T. Galbraith

Keyword(s):

Electron Microscopy ◽

Room Temperature ◽

Bulk Material ◽

Model Structure ◽

Bulk Crystals ◽

Lattice Imaging ◽

Thin Sections ◽

Ferric Oxyhydroxide ◽

Resolution Electron ◽

Hydrolysis Of

Introduction Previously we had suggested (l) that the striations observed in the pod shaped crystals of β FeOOH were an artefact of imaging in the electron microscope. Contrary to this adsorption measurements on bulk material had indicated the presence of some porosity and Gallagher (2) had proposed a model structure - based on the hollandite structure - showing the hollandite rods forming the sides of 30Å pores running the length of the crystal. Low resolution electron microscopy by Watson (3) on sectioned crystals embedded in methylmethacrylate had tended to support the existence of such pores.We have applied modern high resolution techniques to the bulk crystals and thin sections of them without confirming these earlier postulatesExperimental β FeOOH was prepared by room temperature hydrolysis of 0.01M solutions of FeCl3.6H2O, The precipitate was washed, dried in air, and embedded in Scandiplast resin. The sections were out on an LKB III Ultramicrotome to a thickness of about 500Å.

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