Biotin transport by a biotin-deficient strain of escherichia coli

Biotin uptake has been investigated using an Escherichia coli biotin requiring auxotroph grown under biotin-deficient conditions. This strain accumulated biotin in the free and bound form. In agreement with a previous report by O. Prakash and M.A. Eisenberg (J. Bacteriol. 120 (1974) 785–791), the biotin entry proved to be an active process which depended on an energy source and was inhibited in the presence of uncouplers. The kinetic parameters have been determined (K_M = 0.05 μM, V_max = 7 pmol/min per mg dry weight). The pool of free biotin could be readily exchanged with external biotin and decreased to a very low level in the absence of an energy source. The use of several biotin analogues revealed that this transport system was quite specific for biotin: slight modifications, for instance in the valeric chain. lowered drastically the affinity for the carrier.     

Influence du groupe trichloroacéthyle sur les déplacements chimiques des signaux des atomes de carbone du 1,2,3,4,6-penta-O-acéthyl-β-d-glucopyranose et du β-gentiobiose octaacétate en R.M.N.-13C

The influence of the trichloroacetyl group on the ¹³C chemical shift of the substituted and vicinal carbon atoms allows the unambiguous assignment of the signals of the carbon atoms. For derivatives of 1,2,3,4,6-penta-O-acetyl-β-d-glucopyranose and β-gentiobiose octaacetate, the “α-effect” is +4 to +5 p.p.m. (deshielding), whereas the “β-effect” has smaller and always negative values.     

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.     

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.     

Effects of thyroidectomy of the rat on the structure and functions of skeletal muscle mitochondria]

Mitochondria used in the present study were isolated from skeletal muscle of normal and thyroidectomized rats. The preparations were controlled by electron microscopy. It was not possible to find any morphological change induced by thyroidectomy, nevertheless, some difference appeared in the cytochrome contents which were slightly decreased. Oxygen consumption rates of thyroidectomized rat mitochondria were decreased when the particles were maintained in states 3 and 4 in the presence of various substrates, but the P/O ratios were not modified. The activities of mitochondrial enzymes were in general slightly affected by thyroidectomy except for glycerol-1-phosphate cytochrome c reductase and NADH rotenone sensitive cytochrome c reductase which were decreased and for glutamate dehydrogenase activity which was increased. The tRNA nucleotidyltransferase activity found in the mitochondrial matrix was not influenced by the absence of thyroid secretion. Normal rat muscle mitochondria incorporate 14C-leucine with an artificial ATP-generating system or with a respiratory substrate. The amino acid incorporation was decreased by thyroidectomy. Muscle mitochondria analyzed by polyacrylamide gel electrophoresis contained more than 30 protein components with MW ranging from 10.000 to 135.000. Thyroidectomy lowered the amount of a fraction of about 54.000 MW. It is not impossible that all the data observed in the absence of thyroid secretion are in relation with changes induced in the mitochondrial genome as previously shown in mitochondria isolated from liver or thyroidectomized rats.     

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.     

Lipopolysaccharides from thermosensitive mutants of Escherichia coli K12 (author's transl)]

Thermosensitive mutants of Escherichia coli K12 were grown at 30 degrees C and 40 degrees C. The serologic properties and the composition of their lipopolysaccharides were investigated. The inhibition of hemagglutination by the lipopolysaccharides of various mutant strains was tested against the anti-E. coli K12 CR34 system. An inhibition was observed with all the mutants but one, CR34 T83 which had no inhibitory effect. Chemical analysis of lipopolysaccharides and mass spectrometric analysis of their methylated derivatives indicated the presence of the same components in the various lipopolysaccharides: glucose, galactopyranose, galactofuranose, heptopyranose and heptofuranose. However the 2,3,4 tri-O-methyl glucose is missing in the lipopolysaccharide of the mutant T83. This result agrees with the absence of a substituent on the 6-position of the non-reducing core-terminal glucose. The lipopolysaccharide of the T83 mutant has the complete core-type of E. coli K12. The relations of mutations with modifications of the composition of inner and outer envelopes in various mutants are discussed.     

Synthesis by Enzymatic Catalysis VI—An Investigation of Chemical Modification of HRP by Fourier Transform Infra-Red Vibrational Spectroscopy

Horseradish peroxidase was chemically conjugated on its carbohydrate moieties with short aliphatic chains (C₈ and C₁₆). An analytical method using FT.IR spectroscopy was developed to analyze this alteration in enzyme structure. This method is non-destructive, and can be applied directly to samples of the reaction mixture. More general applications of this technique are described and discussed.