Specific interaction between VH and VL regions of human monoclonal immunoglobulins

Preferential reassociation of immunoglobulin H and L chains was investigated using a method of competitive hybridization. A model was built in which two monoclonal light chains, one autologous, L_A, and one heterologous, L_B, were competitively reassociated with a given monoclonal heavy chain, H_A. A total of 12 human myeloma proteins were used with known isotypic, allotypic and variability subgroups: 44 distinct combinations were studied by competitive hybridizations. It was found that a preferential reassociation occurred between the complementary H and L chains that were associated in the native molecule in 80% of the cases. It was clearly established that the subgroups had no influence on the preferential reassociations that seem, therefore, to rely exclusively on individual (“idiotypic”) structural differences. It was shown that, although H and L chains had been fully reduced and denatured, the same degree of preferential reassociation was observed after the chains had been reoxidized and refolded. These experiments suggest, therefore, that the observed preferential reassociations are the consequence of an antigen-independent selection process that must have taken place during the differentiation of the antibody-forming cells.     

An amphibian two-domain ‘big’ neurophysin: conformational homology with the mammalian MSEL-neurophysin/copeptin intermediate precursor shown by trypsin-Sepharose proteolysis

A ‘big’ frog (Rana esculenta) neurophysin, encompassing sequences homologous to mammalian MSEL-neurophysin and copeptin, has been passed through a trypsin-Sepharose column in order to compare its conformation with that of the two-domain intermediate precursor isolated from guinea pig. Whereas the polypeptide possesses 8 arginine residues, only two cleavages were observed located in a putative inter-domain sequence (at Arg-94 and Arg-114). Because free vasotocin has been isolated from the frog, it is assumed that pro-vasotocin has a three-domain conformation similar to that of pro-vasopressin but processing in amphibians involves only one step rather than two steps as in mammals.     

Molecular mechanism of beta-adrenergic receptor blockers with intrinsic sympathomimetic activity

beta-Adrenergic receptor (beta AR) blocking agents with intrinsic sympathomimetic activity (ISA) can induce modest increases in beta AR-stimulated activity, such as rate and force of contraction in cardiac tissue. The molecular basis for this activity has been elusive. Previous studies have suggested that these compounds do not stimulate cyclic AMP (cAMP) formation even though activation of adenylate cyclase is the generally accepted mechanism for beta AR promotion of target cell response. In the current studies, we show that several beta AR antagonists with ISA (dichloroisoproterenol, pindolol, and celiprolol) stimulate cAMP accumulation five-, two-, and threefold, respectively, in S49 lymphoma cells, but only if cells are simultaneously incubated with the diterpene forskolin. The KI values observed for inhibition of isoproterenol-stimulated cAMP accumulation or of beta AR [( 125I]iodocyanopindolol) binding for each of the beta blockers with ISA were comparable in magnitude to their respective EC50 values for forskolin-potentiated cAMP accumulation. The forskolin-potentiated responses of these compounds were abolished by the beta AR-antagonist propranolol. These results indicate that the ISA of beta-blocking drugs most likely results from a modest beta AR-mediated stimulation of adenylate cyclase activity. The results further suggest that treatment of target cells with forskolin provides a means to define partial agonism at receptors that are linked to stimulation of adenylate cyclase.     

Influence of thyroid status on the electrophoretic pattern of rat liver mitochondrial proteins]

Liver mitochondria were isolated from normal and thyroidectomized rats and their protein components analyzed by polyacrylamide gel electrophoresis. In whole mitochondria 35 protein fractions with MW ranging from 10,000 to 135,000 were characterized. In the absence of thyroid hormone secretion, the amount of a MW 54,000 fraction was always decreased. Injection of small doses of 3,5,3'-triiodo-L-thyronine to the thyroidectomized animal restored the quantity of that protein fraction to normal. Isolated outer mitochondrial membranes showed the presence of 20 protein fractions. These fractions revealed no change after thyroidectomy. The mitoplast, which contained 35 fractions, exhibited a decrease of the MW 54,000 component in thyroidectomized rats. The mitoplast was separated into several fractions. Water soluble matrix proteins presented molecular weights ranging between 40,000 and 55,000. Proteins, which were slightly bound to the inner mitochondrial membrane and could be extracted by KCl, presented molecular weights between 25,000 and 45,000. Structural proteins showed a principal specific component of MW equals 23,000. Electrophoretic patterns obtained with these submitochondrial fractions were similar in normal and thyroidectomized animals. The mitoplast fraction which contained the insoluble cytochromes (a, a3, b, c1) was isolated ; its principal constituent, of MW 54,000 was significantly decreased after thyroidectomy. Thus, the lack of thyroid hormone secretion lowered the level of a protein constituent bound to the inner membrane of liver mitochondria. The synthesis of this constituent could be controlled by mitochondrial nucleic acids.     

A large-scale synthesis of somatostatin for clinical use by a novel alternating solution/solid-phase procedure

A large-scale synthesis of somatostatin was developed. A stepwise C→N approach in solution was used, employing N(α)-t-butoxycarbonyl amino acid active esters. The scheme of semipermanent protection utilized 2-(methylsulfonyl)-ethoxycarbonyl for the -amino group of lysine; acetamidomethyl for the β-thiol groups of cysteine; the orange-colored 2-[4-(phenylazo)-phenylsulfonyl]-ethoxy group for the C-terminal carboxy group of cysteine. All condensations and N(α)-deprotections were carried out in homogeneous solution, while isolation and purification of peptides carrying the colored group was achieved by precipitation and washing of the solid products. Thus, the “alternating solution/solid-phase peptide synthesis” combines advantages of both the classical solution synthesis and the Merrifield solid-phase technique. The overall yield was 5%, or 16 g of somatostatin from 100 g of the novel amino acid derivative, N(α)-t-butoxycarbonyl-S-acetamidomethyl- -cysteine 2-[4-(phenylazo)-phenylsulfonyl]-ethyl ester. An improved method for the preparation of S-acetamidomethyl- -cysteine, free of thiazolidine carboxylic acid, is described.