Toad

About: Toad is a research topic. Over the lifetime, 1624 publications have been published within this topic receiving 28732 citations.

Structural and biochemical characterization of toad liver fatty acid-binding protein.

Abstract: Two paralogous groups of fatty acid-binding proteins (FABPs) have been described in vertebrate liver: liver FABP (L-FABP) type, extensively characterized in mammals, and liver basic FABP (Lb-FABP) found in fish, amphibians, reptiles, and birds. We describe here the toad Lb-FABP complete amino acid sequence, its X-ray structure to 2.5 A resolution, ligand-binding properties, and mechanism of fatty acid transfer to phospholipid membranes. Alignment of the amino acid sequence of toad Lb-FABP with known L-FABPs and Lb-FABPs shows that it is more closely related to the other Lb-FABPs. Toad Lb-FABP conserves the 12 characteristic residues present in all Lb-FABPs and absent in L-FABPs and presents the canonical fold characteristic of all the members of this protein family. Eight out of the 12 conserved residues point to the lipid-binding cavity of the molecule. In contrast, most of the 25 L-FABP conserved residues are in clusters on the surface of the molecule. The helix-turn-helix motif shows both a negative and positive electrostatic potential surface as in rat L-FABP, and in contrast with the other FABP types. The mechanism of anthroyloxy-labeled fatty acids transfer from Lb-FABP to phospholipid membranes occurs by a diffusion-mediated process, as previously shown for L-FABP, but the rate of transfer is 1 order of magnitude faster. Toad Lb-FABP can bind two cis-parinaric acid molecules but only one trans-parinaric acid molecule while L-FABP binds two molecules of both parinaric acid isomers. Although toad Lb-FABP shares with L-FABP a broad ligand-binding specificity, the relative affinity is different.

Amiloride and the mode of action of aldosterone on sodium transport across toad bladder and skin

Abstract: The characteristics of the inhibitory influence exerted by amiloride on active sodium transport by toad bladder and skin were taken advantage of to shed additional light on the mechanism whereby hormones-chiefly aldosterone-stimulate sodium transport across such epithelia.

Evidence for involvement of microtubules in the action of vasopressin in toad urinary bladder

Abstract: Colchicine, podophyllotoxin, and vinblastine have been found to inhibit the action of vasopressin on water movement in the toad urinary bladder. Tubulin is the major colchicine binding component of toad bladder epithelial cells, accounting for approximately 3.3% of the total cell protein. More than 99% of the tubulin is found in the soluble fraction after sonication, the remainder is in the particulate fraction. Similar to the characteristics of the binding of colchicine to tubulins from other sources, the binding of colchicine to toad bladder tubulin is temperature- and time-dependent, is inhibited competitively by podophyllotoxin (K i =5.5×10−7 m), and has a binding constant of 1×106 liters/mole at 37°. Binding activity decays according to first-order kinetics and is stabilized by vinblastine. The characteristics of the interactions of colchicine and podophyllotoxin with epithelial cell tubulinin vitro closely parallel the ability of these drugs to inhibit the response to vasopressinin vitro. These results, coupled with those of functional and morphological studies, support the view that the ability, of these drugs to affect vasopressin-induced water movement across toad bladder epithelial cells is related to the depolymerization of cytoplasmic microtubules.