Non-Newtonian Behavior of Blood in Oscillatory Flow

Sinusoidal oscillatory flow of blood and of aqueous glycerol solutions was produced in rigid cylindrical tubes. For aqueous glycerol, the amplitude of the measured pressure gradient wave form conformed closely to that predicted by Womersley's theory of oscillatory flow, up to Reynolds numbers approaching 2000. Blood differed significantly from aqueous glycerol solutions of comparable viscosity, especially at low frequencies and high hematocrits. As frequency increased, the hydraulic impedance of blood decreased to a minimum at a frequency of about 1-2 CPS, increasing monotonically at higher frequencies. The dynamic apparent viscosity of blood, calculated from Womersley's theory, decreased with increasing flow amplitude. The reactive component of the hydraulic impedance increased with frequency as predicted by theory; the resistive component decreased with increasing frequency, differing from the resistance of a Newtonian fluid which increased with frequency.     

Involvement of an Inducible Cytochrome P-450 in Precocene II Oxidation by Streptomyces Griseus

Streptomyces griseus oxidizes the insecticide precocene II to its cis- and trans-dihydrodiols and 3-chromenol after growth on an enriched medium containing soybean flour. Oxidation of precocene II is dependent on the level of cytochrome P-450 in this organism. Extracts of cells grown on media lacking soybean flour were devoid of cytochrome P-450 and could not oxidize precocene II. In an in vitro reconstituted system containing NADPH, spinach ferredoxin reductase, spinach ferredoxin and ammonium sulfate fractions enriched in cytochrome P-450, precocene II was oxidized to its dihydrodiols. An aerial mycelium-negative variant of S. griseus (AMY mutant), that was unable to elicit cytochrome P-450 when grown on soybean flour-enriched medium, failed to oxidize precocene II.     

The plasma membrane of myxosporidian valve cells: freeze fracture data

Freeze fracturing of Myxosporidian spores reveals the occurrence of a continuous layer of transmembrane particles all over the surface area of the valve cells which form the spore envelope. These particles are densely packed all over the P face membrane. Due to their polygonal outline, their diameter (6-7 nm) and their central core, they resemble the particles forming the connections of gap junctions which metabolically couple the neighboring cells in animal tissues. In the present report, the role of the transmembrane particles is still hypothetical. However, they might represent a membrane structural specialization of the spores which are submitted to osmotic variations of the fluid external medium. Furthermore similar transmembrane particles are observed at the level of the septate junction which seals the valve cells. In this occurrence, they are arranged in a series of 40 double rows parallel to the suture of the spore envelope. These findings support the view that Myxosporidia are Metazoa and raise the problem of their origin.     

Protein engineering by cDNA recombination in yeasts: shuffling of mammalian cytochrome P-450 functions

We have constructed, in the yeast Saccharomyces cerevisiae, a mosaic assembly of genes by in vivo recombination of partially homologous sequences. The approach was tested on cDNAs encoding functionally distinct mammalian cytochromes P-450 (P-450). The selection for recombinant cDNAs used the transformation of yeast cells, which required the recircularization of a linearized plasmid by recombination of two partially homologous cDNAs. Libraries of mosaic genes with bipartite or tripartite structures were generated by intramolecular and intermolecular recombination events. The presence of yeast promoter and terminator sequences on the flanking sides of the recombined cDNAs has allowed the synthesis of encoded mosaic proteins. A library of yeast clones producing recombinant mouse P-450 P1 and rabbit P-450 LM4 was screened using functional criteria to identify chimeras with shuffled substrate specificity. Restriction mapping of mosaic genes, biochemical analysis of the synthesized proteins, comparison of chimeric enzymes, and the alignment of sequences with bacterial P-450 camphor hydroxylase of known three-dimensional structure, all suggest that the P-450 P1 amino acid residues 203-238 play a major role in the control of cytochrome activity toward carcinogenic polycyclic aromatic hydrocarbons. Similar approaches to structure-function analysis are believed to be applicable to other protein families.     

Degradation of the metal-cyano complex tetracyanonickelate(II) by cyanide-utilizing bacterial isolates

Ten bacterial isolates capable of growth on tetracyanonickelate(II) [K2[Ni(CN)4]] (TCN) as the sole nitrogen source were isolated from soil, freshwater, and sewage sludge enrichments. Seven of the 10 were identified as pseudomonads, while the remaining 3 were classified as Klebsiella species. A detailed investigation of one isolate, Pseudomonas putida BCN3, revealed a rapid growth rate on TCN (generation time, 2 h), with substrate removal and growth occurring in parallel. In addition to TCN, all isolates were able to utilize KCN, although the latter was significantly more toxic; MICs ranged from 0.2 to 0.8 mM for KCN and greater than or equal to 50 mM for TCN. While growth occurred over a wide range of TCN concentrations (0.25 to 16 mM), degradation was most substantial under growth-limiting conditions and did not occur when ammonia was present. In addition, cells grown on TCN were found to accumulate nickel cyanide [Ni(CN)2] as a major biodegradation product. The results show that bacteria capable of growth on TCN can readily be isolated and that degradation (i) appears to parallel the capacity for growth on KCN, (ii) does not occur in the presence of ammonia, and (iii) proceeds via the formation of Ni(CN)2 as a biological metabolite.     

Interaction of antimicrobial dermaseptin and its fluorescently labeled analogues with phospholipid membranes.

Dermaseptin, a 34 amino-acid residue antimicrobial polypeptide [Mor, A., Nguyen, V. H., Delfour, A., Migliore-Samour, D., & Nicolas, P. (1991) Biochemistry 30, 8824-8830] was synthesized and selectively labeled at its N-terminal amino acid with either 7-nitrobenz-2-oxa-1,3-diazole-4-yl (NBD), rhodamine, or fluorescein. The fluorescent emission spectra of the NBD-labeled dermaseptin displayed a blue-shift upon binding to small unilamellar vesicles (SUV), reflecting the relocation of the fluorescent probe to an environment of increased apolarity. Titrations of solutions containing NBD-labeled dermaseptin with SUV composed of zwitterionic or acidic phospholipids were used to generate binding isotherms, from which were derived surface partition constants of (0.66 +/- 0.06) x 10(4) M-1 and (2.8 +/- 0.3) x 10(4) M-1, respectively. The shape of the binding isotherms, as well as fluorescence energy transfer measurements, suggests that some aggregation of membrane-bound peptide monomers occurs in acidic but not in zwitterionic vesicles. The preferential susceptibility of the peptide to proteolysis when bound to zwitterionic but not to acidic SUV suggests that these aggregates might then penetrate a relatively short distance into the hydrophobic region of the acidic membrane. Furthermore, the results provide good correlation between the peptide's strong binding and its ability to permeate membranes composed of acidic phospholipids, as revealed by a dissipation of diffusion potential and a release of entrapped calcein from SUV.     

Transcobalamin II--cobalamin binding sites are present on rabbit germ cells.

Specific binding sites for rabbit transcobalamin II have been found on isolated adult rabbit germ cells. Scatchard analysis revealed a single class of binding sites for [57Co]cyanocobalamin-transcobalamin II with an association constant (Ka) of 1.3 x 10(10) M-1 and 700 sites per cell. Binding was reversible, saturable and calcium dependent. Electron microscope radioautography following incubation with iodinated transcobalamin II at 4 degrees C led to a detectable labeling mainly restricted to the plasma membrane.     

Expression of the E. coli nadB gene and characterization of the gene product L-aspartate oxidase

Quinolinic acid is synthesized in E. coli by the enzymes L-aspartate oxidase and quinolinate synthase A, the genes of which are named nadB and nadA. In our previous work we cloned and characterized the two genes (Flachmann, R., Kunz, N., Seifert, J., Gütlich, M., Wientjes, F.J., L?ufer, A. & Gassen, H.G. (1988) Eur. J. Biochem. 175, 221-228). Here we report on the expression of the nadB gene under control of the inducible left promoter of the bacteriophage lambda. The yield of the active gene product L-aspartate oxidase was enhanced up to 20% of the soluble cell protein. The enzyme was purified to homogeneity in a three-step procedure and the reading frame of the L-aspartate oxidase gene was confirmed by Edman degradation of five cyanogen bromide peptides. L-Aspartate oxidase shows no classical Michaelis-Menten behaviour but is subject to a substrate inactivation. The apparent Km values were different for substrate concentrations below and above 1mM and were determined to 0.5 mM and 4.1mM, respectively. The active form of the enzyme is a monomer of 60,284 Da and contains one molecule of FAD and nine cysteine residues, four of which built up two disulfide bonds. The isoelectric point of the protein was determined to be at pH 5.6. Chemical modifications of the enzyme showed that at least one tyrosine and one histidine residue are essential for enzyme activity. The coenzyme-binding domain is located in the amino-terminal part of the polypeptide chain as revealed by a sequence comparison to other dinucleotide binding enzymes. Furthermore, there is evidence for a relationship to fumarate reductase and succinate dehydrogenase of E. coli.