Antibiotic production by the marine photosynthetic bacterium Chromatium purpuratum NKPB 031704: localization of activity to the chromatophores

Abstract Over 200 strains of marine purple photosynthetic bacteria were isolated. Two strains showed antibiotic activity towards Saccharomyces cerevisiae and were tentatively identified as Chromatium purpuratum . Crude antibiotic, prepared by solvent extraction, showed a broad antimicrobial spectrum. The highest activity was found in the chromatophore fraction. Chromatographic separation of purified light harvesting complex from one strain, NKPB 031704, showed the presence of two separate pigmented compounds which were responsible for antimicrobial activity. Our findings reveal the unexpected ability of photosynthetic bacteria to produce broad spectrum antibiotics. In addition, this is the first example of intracellular localization of antibiotic activity in a marine bacterium.     

Candida albicans and three other Candida species contain an elongation factor structurally and functionally analogous to elongation factor 3.

A cell-free poly(U)-dependent translation elongation system from Candida albicans is ATP-dependent due to the presence of an elongation factor 3 (EF3)-like activity. Saccharomyces cerevisiae ribosomes added to a C. albicans postribosomal supernatant (PRS) supported poly(U)-dependent elongation, suggesting that the C. albicans lysate contained a soluble translation factor functionally analogous to the S. cerevisiae translation factor EF-3. The presence of EF-3 in C. albicans was confirmed by Western blotting using an antibody raised against S. cerevisiae EF-3. This antibody was also used to screen a selection of Candida species, all of which possessed EF-3 with molecular mass in the range of 110-130 kDa.     

Identification of a cysteine residue as the binding site for the dipyrromethane cofactor at the active site of Escherichia coli porphobilinogen deaminase

The dipyrromethane cofactor of Escherichia coli porphobilinogen deaminase was specifically labelled with 13C by growth of the bacteria in the presence of 5-amino[5-13C]levulinic acid. Using 13C-NMR spectroscopy, the structure of the cofactor was confirmed as a dipyrromethane made up of two linked pyrrole rings each derived from porphobilinogen. The chemical shift data indicate that one of the pyrrole rings of the cofactor is covalently linked to the deaminase enzyme through a cysteine residue. Evidence from protein chemistry studies suggest that cysteine-242 is the covalent binding site for the cofactor.     

The use of the rat hepatoma cell line MH1C1 to investigate the stimulus-secretion response of hepatic acute phase proteins

The rat hepatoma cell line MH1C1 has been characterized to show a stimulated secretion of C-reactive protein in response to both leukocyte supernatant and a purified human interleukin-1 preparation. The time-dependency and dose-response relationship of CRP secretion were comparable to and somewhat more sensitive than the effects of leukocyte supernatant and purified human interleukin-1 on the proliferative rate of murine thymocytes; the proliferative rate of the hepatoma cell line MH1C1 was unchanged under these conditions. Agents which affect the thymocyte bioassay response to interleukin-1 namely interleukin-2, lipopolysaccharide, concanavalin A and phytohemagglutinin showed no effect on the C-reactive protein release of the MH1C1 cell line. These data strongly support the suitability of this cell line for the in vitro study of the hepatic acute phase stimulus-secretion response.     

Purification and characterization of an inhibitor of plasminogen activator released by rat mammary adenocarcinoma cells

An inhibitor of plasminogen activator (PA) secreted by a tumorigenic, but non-metastatic, rat mammary adenocarcinoma cell line has been purified to apparent homogeneity and characterized. It strongly inhibited human urokinase, but was 100 times less potent in inhibiting bovine trypsin and had no effect on plasmin or thrombin. A secreted, urokinase-type PA (Mr 48 000) and a cell-associated PA from a metastatic rat adenocarcinoma cell line were also strongly inhibited. In contrast, a tissue-type PA (Mr 66 000), secreted by human melanoma cells, was only slightly inhibited. Purified inhibitor showed a band of Mr 66 000 in sodium dodecyl sulphate/polyacrylamide gel electrophoresis and an isoelectric point of 4.5 after chromatofocusing. The inhibition of human urokinase was non-competitive.     

The localisation of an Mr 74,000 major chromatin antigen on native salivary chromosomes of Drosophila melanogaster

An antigen making a major contribution to the immune response to Drosophila melanogaster chromatin resides primarily on a nonhistone charge-class family of proteins of Mr 74,000. Immunofluorescence detects this antigen at interbands, puffs and diffuse bands of D. melanogaster salivary chromosomes isolated without exposure to acid fixatives, and on nucleoplasmic ribonucleoprotein droplets. In the electron microscope, gold labelling reveals the binding of monoclonal antibodies specific for the antigen at chromosomal loci generally bearing putative ribonucleoprotein (RNP) particles. However, the locus 3C 11–12 is remarkable in that it bears putative RNP particles but is virtually unlabelled, suggesting protein specificity at different active loci.     

Characterization of the platelet agglutinating activity of thrombospondin

Thrombospondin (TSP) is a glycoprotein secreted from the alpha-granules of platelets upon activation. In the presence of divalent cations, the secreted protein binds to the surface of the activated platelets and is responsible for the endogenous lectin-like activity associated with activated platelets. Platelets fixed with formaldehyde following activation by thrombin are agglutinated by exogenously added TSP. Fixed, nonactivated platelets are not agglutinated. The platelet agglutinating activity of TSP is optimally expressed in the presence of 2 mM each of Mg2+ and Ca2+. Reduction of the disulfide bonds within the TSP molecule inhibits its platelet agglutinating activity. TSP bound to the surface of fixed, activated platelets can be eluted by the addition of disodium ethylenediaminetetraacetate. This approach was exploited to identify the region of the TSP molecule containing the platelet binding site. The binding site resides within a thermolytic fragment of TSP with Mr 140 000 but is not present in the Mr 120 000 fragment derived from the polypeptide of Mr 140 000. Since both the Mr 140 000 and 120 000 fragments contain fibrinogen binding sites, this finding suggests that the binding of TSP to the platelet surface requires interaction with other platelet surface components in addition to fibrinogen. The observation that fibrinogen only partially inhibits the TSP-mediated agglutination of fixed, activated platelets is consistent with this interpretation.     

Adenine nucleotide translocase-dependent anion transport in pea chloroplasts

Pea chloroplasts were found to take up actively ATP and ADP and exchange the external nucleotides for internal ones. Using carrier-free [¹⁴C]ATP, the rate of nucleotide transport in chloroplasts prepared from 12–14-day-old plants was calculated to be 330 μmol ATP/g chlorophyll/min, and the transport was not affected by light or temperature between 4 and 22°C. Adenine nucleotide uptake was inhibited only slightly by carboxyatractylate, whereas bongkrekic acid was nearly as effective an inhibitor of the translocator in pea chloroplasts as it was in mammalian mitochondria. There was no counter-transport of adenine nucleotides with substrates carried on the phosphate translocator including inorganic phosphate, 3-phosphoglycerate and dihydroxyacetone phosphate. However, internal or external phosphoenolpyruvate, normally considered to be transported on the phosphate carrier in chloroplasts, was able to exchange readily with adenine nucleotides. Furthermore, inorganic pyrophosphate which is not transported by the phosphate carrier initiated efflux of phosphoenolpyruvate as well as ATP from the chloroplast. These findings illustrate some interesting similarities as well as differences between the various plant phosphate and nucleotide transport systems which may relate to their role in photosynthesis.     

Studies on the maintenance of cytochromes P-450 and b5, monooxygenases and cytochrome reductases in primary cultures of rat hepatocytes

The cytochrome P-450 content of rat hepatocytes declined rapidly over 72 h in culture, due primarily to denaturation to cytochrome P-420. Six different media were investigated for their ability to conserve cytochrome P-450 during culture, and the most successful was a modified Earle's medium. After 72 h culture in this medium, cytochromes P-450 and b5, NADH-cytochrome b5- and NADPH-cytochrome c-reductases were maintained at 40, 100, 35 and 52% of fresh cell values, respectively. Cytochrome P-450 showed differential functional stability during culture with ethoxyresorufin O-deethylation being more stable than either pentoxyphenoxazone O-depentylation or biphenyl 4-hydroxylation. Monooxygenase than did cytochrome P-450 content. This discrepancy was not explained by loss of flavin nucleotides, FMN or FAD.     

Mapping of epitopes for monoclonal antibodies against human platelet thrombospondin with electron microscopy and high sensitivity amino acid sequencing

A panel of monoclonal antibodies (Mab's) has been raised against human platelet thrombospondin (TSP). One Mab, designated A2.5, inhibits the hemagglutinating activity of TSP and immunoprecipitates the NH2 terminal 25 kD heparin binding domain of TSP (Dixit, V.M., D. M. Haverstick, K. M. O'Rourke, S. W. Hennessy, G. A. Grant, S. A. Santoro, and W. A. Frazier, 1985, Biochemistry, in press). Another Mab, C6.7, blocks the thrombin-stimulated aggregation of live platelets and immunoprecipitates an 18-kD fragment distinct from the heparin binding domain (Dixit, V. M., D. M. Haverstick, K. M. O'Rourke, S. W. Hennessy, G. A. Grant, S. A. Santoro, and W. A. Frazier, 1985, Proc. Natl. Acad. Sci. 82: 3472-3476). To determine the relative locations of the epitopes for these Mabs in the three-dimensional structure of TSP, we have examined TSP-Mab complexes by electron microscopy of rotary-shadowed proteins. The TSP molecule is composed of three 180-kD subunits, each of which consists of a small globular domain (approximately 8 nm diam) and a larger globular domain (approximately 16 nm diam) connected by a thin, flexible strand. The subunit interaction site is on the thin connecting strands, nearer the small globular domains. Mab A2.5 binds to the cluster of three small domains, indicating that this region contains the heparin binding domain and thus represents the NH2 termini of the TSP peptide chains. Mab C6.7 binds to the large globular domains on the side opposite the point at which the connecting strand enters the domain, essentially the maximum possible distance from the A2.5 epitope. Using high sensitivity automated NH2 terminal sequencing of TSP chymotryptic peptides we have ordered these fragments within the TSP peptide chain and have confirmed that the epitope for C6.7 in fact lies near the extreme COOH terminus of the peptide chain. In combination with other data, we have been able to construct a map of the linear order of the identified domains of TSP that indicates that to a large extent, the domains are arranged co-linearly with the peptide chain.