J. Christophe

Primary structure of helodermin, a VIP-secretin-like peptide isolated from Gila monster venom

The complete amino acid sequence of helodermin isolated from the venom of Gila monster was elucidated. The peptide was shown to be a basic pentatriacontapeptide amide: His‐Ser‐Asp‐Ala‐Ile‐Phe‐Thr‐Gln‐Gln‐ Tyr‐Ser‐Lys‐Leu‐Leu‐Ala‐Lys‐Leu‐Ala‐Leu‐Gln‐Lys‐Tyr‐Leu‐Ala‐Ser‐Ile‐Leu‐Gly‐Ser‐Arg‐Thr‐Ser‐Pro‐Pro‐Pro‐NH2. A high degree of sequence similarities to secretin/VIP/PHI/(PHM)/GRF from mammal and bird was observed over the entire N‐terminal 1–27 sequence. In particular, the amino acid residues in positions 3, 6 and 7 were found to be common to 9 peptides of the family. Another interesting feature of the structure of helodermin was its C‐terminal ‐Pro‐Pro‐Pro‐NH2 sequence. Isolation of helodermin was the first demonstration of the existence of a secretin/VIP‐related peptide in an animal that is neither mammal nor bird.

On human pancreatic triacylglycerol lipase: Isolation and some properties

Abstract A single triacylglycerol lipase (EC 3.1.1.3) containing approx. 420 amino acid residues has been purified from human pancreatic juice with a 30% overall yield. The method involved column chromatography on Sephadex G-25, diethylaminoethyl-cellulose, carboxymethyl-cellulose and Sephadex G-75. The molecular weight of the enzyme was estimated to be 46 000 from the amino acid composition. The purified preparation was incapable of catalyzing a prolonged hydrolysis of tributyrin at 25 °C, because of rapid inactivation. The addition of sodium taurodeoxycholate exerted a protective effect on lipase, an inhibitory action on lipolysis, and a shift of the optimal pH down to pH 7.5. Increasing the NaCl concentration enhanced the inhibitory effect of the bile salt, whereas bovine colipase and serum albumin prevented this effect. Only colipase was able to ensure a maximal reaction rate, both in the presence or absence of sodium taurodeoxycholate. Our data indicate that each molecule of human triacylglycerol lipase can easily react with one molecule of bovine colipase, and less easily with two or more molecules.

Helodermin has a VIP-like effect upon canine blood flow

The effect of helodermin on vascular physiology was studied in anesthetized dogs using a synthetic replicate of helodermin and helodermin related peptides. Intraarterial infusion of helodermin caused a dose-dependent increase in femoral blood flow. Helodermin was 16 times less potent than VIP and 5 times more potent than PHM (human PHI). The helodermin effect lasted significantly longer; the half-life of the helodermin effect was 6.5 times longer than VIP. Synthetic helodermin (Hd) N-terminal fragment Hd(1-27)NH2 retained substantial activity similar to the full helodermin molecule but the prolonged effect was lost. Hd(7-35) and Hd(22-35) were inactive in this system. Intravenous injection of synthetic helodermin produced prolonged systemic hypotension and tachycardia; and, similar to VIP, it increased the common carotid arterial blood flow while those of the superior mesenteric and femoral arteries were decreased. The results demonstrate the VIP-like vasodilating activity and cardiovascular effects of helodermin in anesthetized dogs.

VIP and related peptides induce rapid homologous desensitization in the human lymphoma SUP T1 cell line

Incubation of human SUP T1 lymphoblasts with VIP, helodermin and related peptides induced homologous desensitization within 5 min as indicated by: 1) a secondary decrease in cellular cyclic AMP levels, even in the presence of phosphodiesterase inhibitors, 2) a reduced capacity of cells to bind [125I]helodermin, 3) decreased helodermin stimulation of adenylate cyclase activity in membranes, and 4) unaffected NaF- and Gpp[NH]p-stimulated adenylate cyclase activities. The desensitizing ability of all peptides correlated with their efficacy to occupy cell receptors, except for [D-Phe2]VIP, a partial VIP agonist with low intrinsic activity, that did not desensitize.

The Biorder Polytope

Biorders, also called Ferrers relations, formalize Guttman scales. Irreflexive biorders on a set are exactly the interval orders on that set. The biorder polytope is the convex hull of the characteristic matrices of biorders. Its definition is thus similar to the definition of other order polytopes, the linear ordering polytope being the proeminent example. We investigate the combinatorial structure of the biorder polytope, thus obtaining a complete linear description in a specific case, and the automorphism group in all cases. Moreover, a class of facet-defining inequalities defined from weighted graphs is thoroughly analyzed. A weighted generalization of stability-critical graphs is presented, which leads to new facets even for the well-studied linear ordering polytope.

One-step isocratic high-performance liquid chromatographic purification of radioiodinated and radioiodinated-photoactivable derivatives of cholecystokinin

N-Hydroxysuccinimidyl-3-(4-hydroxy-3-[125I]iodophenyl)propionate (the Bolton-Hunter reagent) was conjugated with (Thr 34, NLeu 37) cholecystokinin (CCK) 31-39 in anhydrous dimethylformamide-pyridine in 20% yield. The radiolabelled peptide was purified from the reaction mixture in one step, by isocratic elution from a C18 high-performance liquid chromatographic (HPLC) column with 35% aqueous acetonitrile-0.13% heptafluorobutyric acid as eluent. The concentration of the radiolabelled peptide was estimated by UV monitoring. The acylating photoactivable radioiodinated reagent N-hydroxysuccinimidyl-N-(4-azido-2-nitrophenyl)-3-[125I]iodotyrosi ne was synthesized, purified on a C18 HPLC column by isocratic elution with 65% acetonitrile-1 mM hydrochloric acid, then conjugated with (Thr 34, NLeu 37) CCK31-39. The resulting photoactivable radioiodinated CCK analogue was purified by isocratic elution on a C18 HPLC column with 39% aqueous acetonitrile-0.1 M triethylamine phosphate (pH 3.5). The binding ability of both tracers and their non-radioactive analogues to CCK receptors was tested on rat pancreatic plasma membranes. As compared to a KD of 4.5 nM for unmodified (Thr 34, NLeu 37) CCK31-39, the KD of the radioiodinated Bolton-Hunter derivative was 3 nM, and that of the photoactivable radioiodinated derivative was 19 nM.

Helodermin stimulates prolactin secretion in the rat.

The effect of helodermin, a member of the secretin/vasoactive intestinal polypeptide (VIP)/peptide histidine isoleucine (PHI) family of peptides, on pituitary prolactin (PRL) secretion was examined in the rat. Either i.c.v. or i.v. injection of helodermin resulted in a dose-related increase in plasma PRL levels in urethane-anesthetized male rats. At the doses tested the potency of helodermin to raise plasma PRL levels was greater than that of rat PHI and porcine PHI, and as great as that of VIP.

A comparison of the phosphorylation of Mr = 33k, 21k, and 25k membrane-bound proteins in the rat pancreas, submitted to various secretagogues

The rodent exocrine pancreas is a monodirectional control system where the occupancy of two types of receptors may independently provoke hypersecretion. Specific carbamylcholine and cholecystokinin (CCK-8) receptors, once occupied, stimulate secretion mostly via a phosphatidylinositol- and Ca2+-dependent mechanism (review in Christophe et al., 1980). In addition, carbamylcholine and CCK-8 increase the state of phosphorylation of a particulate protein with Mr = 32 k in isolated mouse pancreatic acini (Burnham & Williams, 1982). The secretory action of secretin receptors in the rat pancreas is clearly differentiated from the action of the first type of receptors and results from a sustained elevation of cyclic AMP and the activation of cyclic AMP-dependent protein kinase(s). In addition, secretin increases the phosphorylation of three particulate proteins with Mr = 29–36 k, Mr = 25 k, and Mr = 21 k (Freedman & Jamieson, 1982; Vandermeers et al., 1984b).

Interaction of synthetic N-and C-terminal fragments of helodermin with rat liver VIP receptors

Synthetic helodermin was more potent than natural helodermin (purified from the venom of Gila monster) in activating adenylate cyclase in rat liver membranes. Two possible reasons for this discrepancy were discussed. Comparing adenylate cyclase activation to the binding of 125I-natural helodermin and 125I-VIP in the presence of six synthetic helodermin fragments (1-27, 7-35, 13-35, 17-35, 18-35 and 22-35), we conclude that the effects of both synthetic and natural helodermin were mediated through an interaction with VIP receptors. The C-terminal (28-35) extension of these peptides favored VIP receptor recognition. Their N-terminal extremity was not necessary for binding and for ensuing adenylate cyclase activation, illustrating again the atypical coupling of VIP receptors with the effector enzymatic system, in rat liver membranes.

The Polytope of m -Subspaces of a Finite Affine Space

The m-subspace polytope is defined as the convex hull of the characteristic vectors of all m-dimensional subspaces of a finite affine space. The particular case of the hyperplane polytope has been investigated by Maurras (1993) and Anglada and Maurras (2003), who gave a complete characterization of the facets. The general m-subspace polytope that we consider shows a much more involved structure, notably as regards facets. Nevertheless, several families of facets are established here. Then the group of automorphisms of the m-subspace polytope is completely described and the adjacency of vertices is fully characterized.