The obligate aerobic bacterium, Vitreoscilla, synthesizes elevated quantities of a homodimeric hemoglobin (VHb) under hypoxic growth conditions. Expression of VHb in heterologous hosts often enhances growth and product formation. A role in facilitating oxygen transfer to the respiratory membranes is one explanation of its cellular function. Immunogold labeling of VHb in both Vitreoscilla and recombinant Escherichia coli bearing the VHb gene clearly indicated that VHb has a cytoplasmic (not periplasmic) localization and is concentrated near the periphery of the cytosolic face of the cell membrane. OmpA signal-peptide VHb fusions were transported into the periplasm in E. coli, but this did not confer any additional growth advantage. The interaction of VHb with respiratory membranes was also studied. The K d values for the binding of VHb to Vitreoscilla and E. coli cell membranes were ϳ5-6 M, a 4 -8-fold higher affinity than those of horse myoglobin and hemoglobin for these same membranes. VHb stimulated the ubiquinol-1 oxidase activity of inverted Vitreoscilla membranes by 68%. The inclusion of Vitreoscilla cytochrome bo in proteoliposomes led to 2.4-and 6-fold increases in VHb binding affinity and binding site number, respectively, relative to control liposomes, suggesting a direct interaction between VHb and cytochrome bo.

In the continuous search for new antiinflammatory agents from natural products, dichloromethane (DCM), ethyl acetate (EtOAc) and methanol (MeOH) extracts of Ipomea fistulosa leaves were evaluated for inhibition of production of nitric oxide (NO), interleukin 1beta (IL-1β) and tumor necrosis factor alpha (TNF-α) in lipopolysaccharide (LPS) stimulated J774A.1 cells. Among the tested extracts, the ethyl acetate (EtOAc) extract was found to be most active and activity based fractionation of this extract by column chromatography led to the identification of seven compounds for the first time from this plant. Furthermore, 3,4-dimethoxy cinnamic acid (1) exhibited two folds more potent inhibition of LPS-induced NO production (IC 50 = 10.7 μg/mL) as compared with the standard, L-NAME (IC 50 =19.8 μg/mL). The present study supports the use of Ipomea fistulosa leaves for the treatment of inflammation.

We developed an ELISA-based method for rapid optimization of various tissue processing parameters in immunogold labeling for electron microscopy. The effects of aldehyde fixation, tannic acid, postfixation, dehydration, temperature, and antigen retrieval on antibody binding activity of Vitreoscilla hemoglobin (VHb) expressed in E. coli cells were assayed by ELISA and the results confirmed by quantitative immunogold labeling transmission electron microscopy (TEM). Our results demonstrated that low concentrations (0.2%) of glutaraldehyde fixation caused minimal loss in total binding compared to higher concentrations. Dehydration in up to 70% ethanol resulted in some distortion of cellular ultrastructure but better antibody binding activity compared to dehydration up to 100%. Postfixation or incorporation of tannic acid in the primary fixative caused almost total loss of activity, whereas antigen retrieval of osmium-postfixed material resulted in approximately 90-100% recovery. The sensitivity of detection of proteins by immunogold labeling electron microscopy depends on the retention of antibody binding activity during tissue processing steps, e.g., fixation and dehydration. Our study indicated that an ELISA-based screening method of various tissue processing procedures could help in rapid selection and optimization of a suitable protocol for immunogold localization and quantification of antigen by TEM.