Purification and characterization of the thermostable ribulose-1,5-bisphosphate carboxylase/oxygenase from the thermophilic purple bacterium Chromatium tepidum

The Calvin cycle enzyme ribulose-bisphosphate carboxylase/oxygenase has been purified and characterized from the thermophilic and obligately anaerobic purple sulfur bacterium, Chromatium tepidum. The enzyme is an L8S8 carboxylase with a molecular mass near 550 kDa. No evidence for a second form of the enzyme lacking small subunits was obtained. C. tepidum ribulose-bisphosphate carboxylase/oxygenase was stable to heating to temperatures of 60 degrees C and could be readily purified in an active form at room temperature. Both carboxylase and oxygenase activities of this enzyme were Mg2+-dependent and carboxylase activity was sensitive to the effector 6-phosphogluconic acid. The Km for ribulose bisphosphate for the carboxylase activity of the C. tepidum enzyme was substantially higher than that observed in mesophilic Calvin cycle autotrophs. Amino acid composition and immunological analyses of C. tepidum and Chromatium vinosum ribulose-bisphosphate carboxylases showed the enzymes to be highly related despite significant differences in heat stability. It is hypothesized that thermal stability of C. tepidum ribulose-bisphosphate carboxylase/oxygenase is due to differences in primary structure affecting folding patterns in both the large and small subunits and is clearly not the result of any unique quaternary structure of the thermostable enzyme.     

The 131I Ortho-iodohippurate Photoscan in Human Renal Allografts

Nine examples, in seven patients, from a large cadaver renal allograft program, illustrate the value of radio-hippuran photoscans in differentiating causes of post-implant oliguria. Hippuran scans are shown to be more valuable than chlormerodrin scans when renal function is acutely depressed. Hippuran scans aided in the decision to remove kidneys in four cases of severe oliguria and to retain kidneys in two others. In two further examples, extravasation of urine was detected by scanning after radio-hippuran injection when other tests had failed to do so.The technique of radio-hippuran scanning has a place in the differentiation of acute and subacute renal dysfunction and has proved particularly valuable in the early oliguric complications of a cadaver renal transplant program.     

Biexponential Kinetics of (R)-α-[3H]Methylhistamine Binding to the Rat Brain H3 Histamine Receptor

The H3 histamine receptor is a high-affinity receptor reported to mediate inhibition of CNS histidine decarboxylase activity and depolarization-induced histamine release. We have used (R)-alpha-[3H]methylhistamine, a specific, high-affinity agonist, to characterize ligand binding to this receptor. Saturation binding studies with rat brain membranes disclosed a single class of sites (KD = 0.68 nM; Bmax = 78 fmol/mg of protein). Competition binding assays also yielded an apparently single class of sites with a rank order of potency for ligands characteristic of an H3 histamine receptor: N alpha-methylhistamine, (R)-alpha-methylhistamine greater than histamine, thioperamide greater than impromidine greater than burimamide greater than dimaprit. In contrast, kinetic studies disclosed two classes of sites, one with fast, the other with slow on-and-off rates. Density of (R)-alpha-[3H]methylhistamine binding followed the order: caudate, midbrain (thalamus and hippocampus), cortex greater than hypothalamus greater than brainstem greater than cerebellum. These data are consistent with an H3 histamine receptor, distinct from H1 and H2 receptors, that occurs in two conformations with respect to agonist association and dissociation or with multiple H3 receptor subtypes that are at present pharmacologically undifferentiated.     

13C-nuclear magnetic resonance spectra of compounds containing β-D-fructofuranosyl groups or residues

¹³C-N.m.r. spectra have been recorded for sucrose, melezitose, levan, inulin, palatinose, and D-fructose. Except for the last, each compound contains a different O-substituted D-fructofuranose residue or group, or β-D-fructofuranosyl residue or group. On the basis of chemical-shift displacements, resulting from O-substitution at specific carbon atoms, resonances can be assigned to the carbon atoms of the β-D-fructofuranosyl residue. Fortuitously, the α-D-glucopyranosyl group present in some of these compounds exhibits resonances that do not obscure the β-D-fructofuranosyl resonances. O-Substitution of the β-D-fructofuranosyl residue causes a downfield displacement of the corresponding, linked-C resonance; however, the other major resonances of this residue are not affected by bulky substituents. Members of a series of levan fractions, the products of partial, acid hydrolysis of Streptoccoccus salivarius levan, were then examined for changes in relative degree of branching.     

A modified protein assay from microgram to low nanogram levels in dilute samples

In this article, we present a modified and improved protein assay that was previously described as “amidoschwarz assay” by Schaffner and Weissmann [13]. Our improved protein assay is user-friendly and 30–40 times more sensitive than the earlier method. The assay was developed into three formats (macro-, micro-, and nanoassay) with trichloroacetic acid (TCA) as protein precipitating agent, measuring up to 96 samples. The macro and micro formats of this assay require a single reagent staining with amido black of protein dots bound to nitrocellulose membrane with lowest protein measurements to 1 and 0.1 μg, respectively. On the other hand, the nanoassay, with combination staining of amido black followed by colloidal gold, can extend the detection limit to 2.5 ng of protein. Protein concentrations were determined by densitometry and/or spectrophotometry. This assay is compatible with many ionic and non-ionic detergents. This improved protein assay provides an additional choice to researchers in measuring total protein concentration accurately in dilute biological samples as low as 0.125 μg/ml prior to their biochemical analysis such as in comparative proteomics.     

Microenvironment-induced TIMP2 loss by cancer-secreted exosomal miR-4443 promotes liver metastasis of breast cancer

We aimed to investigate the role of exosomal miR-4443 in metastasis of breast cancer (BCa). In vitro wound-healing assay and transwell invasion assay were used to investigate effect of miR-4443 on BCa cells. Animal experiments were performed to confirm its effects in vivo. miR-4443 promotes the metastasis of BCa cells through downregulating tissue inhibitors of metalloproteinase 2 (TIMP2) and upregulating matrix metalloproteinases (MMPs). Highly invasive BCa cells have a higher expression of miR-4443 in both cells and exosomes. The exosomes derived from highly invasive BCa cells mainly gather in the primary tumor and liver. In vivo, overexpression of miR-4443 in noninvasive BCa cells induces liver metastasis, accompanied with downregulated TIMP2, and upregulated MMP-2 in both the primary tumor and liver. When we armed MCF-10A exosomes with miR-4443 inhibitors to treat mice bearing high-miR-4443 tumors, exosomes accumulated in the primary tumor, and liver following the upregulation of TIMP2 and downregulation of MMP2, and the metastasis was inhibited. Highly invasive BCa cells destroy natural barriers against metastasis by delivering exosomal miR-4443 to stromal cells of the primary tumor and impairing TIMP2, consequently activating MMP; circulating exosomal miR-4443 might promote BCa cells lodging in future metastatic sites through the similar mechanisms.