A membrane-bound protein inhibitor of the high affinity Ca ATPase in rat liver plasma membranes.

Pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) and PACAP-27 are recently characterized hypothalamic peptides with marked homology with vasoactive intestinal peptide (VIP), which are concentrated in the innervation of the digestive tract. We now report that, on rat liver plasma membranes, PACAP interacts with at least two types of receptors: receptors demonstrating equally high affinity for PACAP and VIP and receptors with high affinity for PACAP but low affinity for VIP. In contrast, on rat intestinal epithelial cell laterobasal membranes, only receptors with high affinities for PACAP and VIP were observed. After 125I-labeled VIP or 125I-labeled PACAP-27 was cross-linked to the liver plasma membrane receptors with the use of either disuccinimidosuberate or disuccinimido dithiobis(propionate), analysis of the resulting ligand-receptor complexes on sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the structures of the VIP and PACAP receptors were similar: both ligand-receptor complexes displayed two radioactive bands with relative molecular weights of 80,000 and 56,000 under reducing conditions and of 75,000 and 53,000 under nonreducing conditions. These findings suggest that the receptors for the PACAP peptides and VIP are closely related, reflecting the marked homology between these peptides. The presence of receptors specific for PACAP on rat liver plasma membranes should stimulate further studies of the interaction between PACAP and the liver.

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A high affinity Ca2+-ATPase in rat liver plasma membranes

The Japanese Journal of Pharmacology ◽

10.1016/s0021-5198(19)54099-9 ◽

1982 ◽

Vol 32 ◽

pp. 201

Author(s):

Takafumi Iwasa ◽

Yasushi Iwasa ◽

Eishichi Miyamoto

Keyword(s):

Rat Liver ◽

Plasma Membranes ◽

High Affinity ◽

Liver Plasma Membranes ◽

Rat Liver Plasma Membranes

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Guanine-nucleotide and hormone regulation of polyphosphoinositide phospholipase C activity of rat liver plasma membranes. Bivalent-cation and phospholipid requirements

Biochemical Journal ◽

10.1042/bj2480791 ◽

1987 ◽

Vol 248 (3) ◽

pp. 791-799 ◽

Cited By ~ 85

Author(s):

S J Taylor ◽

J H Exton

Keyword(s):

Phospholipase C ◽

Rat Liver ◽

Plasma Membranes ◽

Maximal Effect ◽

Guanine Nucleotide ◽

Guanine Nucleotide Binding Protein ◽

Liver Plasma Membranes ◽

Rat Liver Plasma Membranes ◽

Membrane Bound ◽

Hydrolysis Of

The effect of the GTP analogue guanosine 5′-[gamma-thio]triphosphate (GTP[S]) on the polyphosphoinositide phospholipase C (PLC) of rat liver was examined by using exogenous [3H]phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]. GTP[S] stimulated the membrane-bound PLC up to 20-fold, with a half-maximal effect at approx. 100 nM. Stimulation was also observed with guanosine 5′-[beta gamma-imido]triphosphate, but not with adenosine 5′-[gamma-thio]triphosphate, and was inhibited by guanosine 5′-[beta-thio]diphosphate. Membrane-bound PLC was entirely Ca2+-dependent, and GTP[S] produced both a decrease in the Ca2+ requirement and an increase in activity at saturating [Ca2+]. The stimulatory action of GTP[S] required millimolar Mg2+. [8-arginine]Vasopressin (100 nM) stimulated the PLC activity approx. 2-fold in the presence of 10 nM-GTP[S], but had no effect in the absence of GTP[S] or at 1 microM-GTP[S]. The hydrolysis of PtdIns(4,5)P2 by membrane-bound PLC was increased when the substrate was mixed with phosphatidylethanolamine, phosphatidylcholine or various combinations of these with phosphatidylserine. With PtdIns(4,5)P2, alone or mixed with phosphatidylcholine, GTP[S] evoked little or no stimulation of the PLC activity. However, maximal stimulation by GTP[S] was observed in the presence of a 2-fold molar excess of phosphatidylserine or various combinations of phosphatidylethanolamine and phosphatidylserine. Hydrolysis of [3H]phosphatidylinositol 4-phosphate by membrane-bound PLC was also increased by GTP[S]. However, [3H]phosphatidylinositol was a poor substrate, and its hydrolysis was barely affected by GTP[S]. Cytosolic PtdIns(4,5)P2-PLC exhibited a Ca2+-dependence similar to that of the membrane-bound activity, but was unaffected by GTP[S]. It is concluded that rat liver plasma membranes possess a Ca2+-dependent polyphosphoinositide PLC that is activated by hormones and GTP analogues, depending on the Mg2+ concentration and phospholipid environment. It is proposed that GTP analogues and hormones, acting through a guanine nucleotide-binding protein, activate the enzyme mainly by lowering its Ca2+ requirement.

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Catalytic unit-independent phosphorylation and dephosphorylation of type II regulatory subunit of cyclic AMP-dependent protein kinase in rat liver plasma membranes

Biochemical Journal ◽

10.1042/bj2340163 ◽

1986 ◽

Vol 234 (1) ◽

pp. 163-168 ◽

Cited By ~ 5

Author(s):

Z Kiss ◽

Y Luo ◽

G Vereb

Keyword(s):

Cyclic Amp ◽

Rat Liver ◽

Plasma Membranes ◽

Regulatory Subunit ◽

Dependent Protein Kinase ◽

Liver Plasma Membranes ◽

Catalytic Unit ◽

Rat Liver Plasma Membranes ◽

Dependent Protein ◽

Membrane Bound

Rat liver plasma membranes contain a 55 kDa protein which proved to be identical with type II regulatory subunit (RII) of the cyclic AMP-dependent protein kinase (kinase A) by several criteria (gel electrophoretic behaviour, peptide map, position of the autophosphorylated site). Analysis of phosphopeptide maps revealed that the membrane-bound RII was phosphorylated by a kinase which is unrelated to the catalytic unit (C) of kinase A. Dephosphorylation of the membrane-bound RII by an endogenous phosphatase was stimulated by both cyclic AMP and fluoride. Addition of C did not stimulate dephosphorylation even in the presence of ADP; moreover, protein inhibitor of C did not modify the effects of cyclic AMP or fluoride. The effects of both cyclic AMP and fluoride were, however, inhibited by C. Results indicate that rat liver plasma membranes contain a phosphorylation-dephosphorylation system for which RII is a relatively specific substrate.

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