Identification of the purC gene product of Escherichia coli.

The purC region of the Escherichia coli chromosome was isolated from in vivo-derived lambda transducing bacteriophages and cloned in high-copy-number plasmids. The product of the purC gene, phosphoribosylaminoimidazolesuccinocarboxamide synthetase, was identified as a protein with an Mr of ca. 27,000. The level of the protein is increased by more than 60-fold in strains carrying the gene on a high-copy-number plasmid. Purine addition represses the enzyme level in both plasmid- and non-plasmid-containing strains.     

Manipulus Rubiacearum III. Deppeeae,a new tribe of Rubioideae (Rubiaceae)

A new tribe,Deppeeae, in subfamily Rubioideae Verdc. of the Neotropical Rubiaceae is described. It is easily distinguished by the presence of raphides, contorted or modified alternative aestivation of the corolla, numerous small ovules, and placenta attached to the middle of the septum. Three genera are known to be members of the tribe,Deppea, Schenckia, andOmiltemia. A hypothetical phylogenetic tree for the tribe is presented.     

Reply to Claudio Cobelli and Gianna Toffolo,identifiability from parameter bounds. Structural and numerical aspects. Math. Biosci. 71:237–243 (1984)

We present an analysis of receptor mediated endocytosis which includes the following elements: ligand binding to receptors, interaction of the ligand-receptor complex with coated pits, internalization of coated pit contents, recycling of receptors, and degradation of ligand. The model accounts quantitatively for epidermal growth factor binding and clustering in coated pits at 4°C, for its internalization and degradation at 37°C, and for EGF receptor down-regulation. Steady state analysis of the model indicates that the slope and intercept of a Scatchard plot are functions of the kinetic parameters of the endocytic loop and do not necessarily reflect the affinity and number of receptors in metabolically active cells. Moreover, the model predicts that for homogeneous receptors, a Scatchard plot can be either linear or nonlinear, depending on the concentration of proteins in coated pits which interact with ligand-receptor complexes. A slight generalization of the model in which phorbol ester-receptor complexes compete with EGF-receptor complexes for the same coated pit proteins provides a quantitative explanation for the loss of the high affinity portion of the EGF Scatchard plot subsequent to preincubation with phorbol esters. This explanation leads to the prediction of a local homology between a portion of the phorbol ester receptor sequence and a portion of the EGF receptor sequence.     

Cross-linking of B lymphocyte Fc gamma receptors and membrane immunoglobulin inhibits anti-immunoglobulin-induced blastogenesis

The Fc portion of rabbit anti-mouse immunoglobulin (Ig) antibodies interferes with anti-Ig-induced B lymphocyte activation as measured by DNA synthesis on day 3 of culture or maturation to Ig-secreting cells in the presence of soluble helper factors on day 4 or 5. To investigate this Fc-dependent effect at an earlier stage in B cell activation, rabbit IgG anti-mouse mu-chain- or delta-chain-specific antibodies were compared with their F(ab')2 fragments for the ability to induce mouse B cells to undergo blast transformation, as defined by an increase in cell volume during the first 24 hr of culture. Both F(ab')2 anti-Ig reagents induce blast transformation, although F(ab')2 anti-mu antibodies induce a greater size change than F(ab')2 anti-delta antibodies. Whole anti-mu or anti-delta antibodies do not induce blast transformation; however, in the presence of a monoclonal anti-mouse Fc gamma receptor antibody that blocks IgG binding to Fc gamma receptors (Fc gamma R), whole anti-mu or anti-delta antibodies induce blast transformation as well as their F(ab')2 fragments. Because the anti-Fc gamma R antibody alone has no effect on blast transformation, it appears that the simultaneous binding of membrane IgM (or IgD) and Fc gamma R by whole anti-Ig antibodies prevents this early event in membrane Ig-induced B cell activation.     

Comparison of labeled propanediol and urea as markers of lung vascular injury

The purpose of these studies was a comparison of [14C]urea (U) and 1,3-[14C]propanediol (Pr) as measures of lung vascular permeability-surface area (PS) under base-line conditions and after lung injury caused by alloxan infusion in isolated perfused dog lungs. Indicator mixtures of 125I-albumin, 51Cr-red blood cells, 3HOH, and U or Pr were injected under base-line conditions, after 1.2 g of alloxan, and after an additional 0.8 g of alloxan. Indicator-dilution curves were analyzed from sampled outflow blood to provide PS, the square root of effective extravascular diffusivity multiplied by exchange surface area (D1/2S), and extravascular lung water (EVLW) from the tracer mean transit times (VW). Results show that alloxan increases PS and D1/2S for U, D1/2S for Pr, and VW and EVLW by desiccation. All indicator-dilution parameters correlate significantly with alloxan dose. Interpretation of Pr transport suggests that materials with lipid and hydrophilic pathways might be used in conjunction with U to minimize the effects of surface area changes and increase the sensitivity of these tracers to permeability alteration. In addition Pr may be a useful alternative to U as a marker of vascular damage.     

Neurotensin and substance P receptors expressed in Xenopus oocytes by messenger RNA from rat brain

Xenopus oocytes were induced to acquire sensitivity to neurotensin and substance P, by injecting them with a fraction of poly(A)+ mRNA from rat brain. Non-injected oocytes, and oocytes injected with other brain mRNAs, failed to show responses, suggesting that receptors to these peptides were expressed by specific brain mRNAs. Responses to substance P and neurotensin comprised an oscillatory chloride current, and a smooth current having different ionic basis. These currents resembled those seen during activation of muscarinic and serotonergic receptors, but were not blocked by the corresponding antagonists atropine and methysergide. The responses to substance P, and to a lesser extent to neurotensin, showed a long-lasting desensitization. Similarities between the oscillatory currents evoked by the peptides acetylcholine and serotonin suggest that all these receptors may 'link in' to a common intracellular messenger pathway.     

Enzyme-linked immunosorbent assay for secalonic acid D

A competitive enzyme-linked immunosorbent assay was developed for the xanthone dimer secalonic acid D. The immunogen and enzyme marker were prepared by direct reaction of secalonic acid D with bovine serum albumin and horseradish peroxidase, respectively. The resultant conjugates were characterized by UV/VIS spectra and thin layer chromatography. The hapten:protein ratios in the conjugates were estimated by difference UV/VIS spectra and by fluorescent techniques. Immunization procedures were conducted utilizing New Zealand rabbits over a period of 12 weeks. The competitive enzyme-linked immunosorbent assay on microtiter plates showed that secalonic acid D was detectable within a range of 250–25 000 ng/assay.     

Dye coupling in the organ of Corti

Summary Dye-coupling in an in vitro preparation of the supporting cells of the guinea-pig organ of Corti was evaluated by use of the fluorescent dyes, Lucifer Yellow, fluorescein and 6 carboxyfluorescein. Despite the presence of good electrical coupling in Hensen cells (coupling ratios >0.6) the spread of Lucifer yellow was inconsistent. Hensen cells are very susceptible to photoinactivation, i.e., cell injury upon illumination of intracellular dye; and this in conjunction with Lucifer Yellow's charge and K+-induced precipitability may account for its variability of spread. Fluorescein and 6 carboxyfluorescein, on the other hand, spread more readily and to a greater extent than Lucifer Yellow, often spreading to cell types other than those of Hensen. Dye spread is rapid, occurring within a few minutes. These results suggest that molecules of metabolic importance also may be shared by the supporting cells of the organ of Corti.