Mechanism of the binding of 2-(4'-hydroxyphenylazo)benzoic acid to bovine serum albumin

The mechanism of the binding of 2-(4'-hydroxyphenylazo)benzoic acid (HABA) to bovine serum albumin was studied by relaxation methods as well as the binding isotherm using gel chromatography. A single relaxation was observed over a wide range of HABA concentration except at the extremes of high concentration where another slow process was observed. The concentration dependence of the reciprocal relaxation time of the fast process decreased monotonically with increase in concentration of HABA at constant polymer concentration. The data were analyzed on the basis of Brown's domain structure model and were found to be consistent with a sequential binding mechanism. The azohydrazon tautomerism of HABA was identified with the intramolecular step of the complex. The activation parameters of the step, determined from the temperature dependence of the relaxation time of the fast process, showed that this step is rate limited by an enthalpy barrier in both forward and backward directions. Comparison of the activation parameters with those of other serum albumin-ligand systems suggests that there is an enthalpy-entropy compensation in the activation process of the intramolecular step with the compensation temperature at about 270 K; the enthalpy-entropy compensation is thought to be related to the hydrophobic nature of the ligand.     

Further new species of the plant bug genus Campylomma Reuter from the Oriental Region (Heteroptera: Miridae: Phylinae: Nasocorini)

The fauna of the nasocorine plant bug genus Campylomma Reuter from the Oriental Region, including subtropical Japanese Ryukyu Islands (Okinawa Island of Southwest Islands-group) and Taiwan is updated. Three new species are herein described, C. astica n. sp. (from Okinawa and Taoyuan, Taiwan), C. hibiscicola n. sp. (Bangkok, Thailand) and C. nanrenana n. sp. (Pingtung, Taiwan). Of these, C. astica and C. hibiscicola, were observed to have cryptic habitat-preference, inhabiting bracts, stipules or flower buds of the sea (or coastal) hibiscus, Hibiscus tiliaceus (L.) (Malvaceae), planted for landscaping at urbanized zones. An updated checklist of the 22 Oriental Campylomma species is provided.     

Sequence dependence of DNA conformational flexibility

By using conformational free energy calculations, we have studied the sequence dependence of flexibility and its anisotropy along various conformational variables of DNA base pairs. The results show the AT base step to be very flexible along the twist coordinate. On the other hand, homonucleotide steps, GG(CC) and AA(TT), are among the most rigid sequences. For the roll motion that would correspond to a bend, the TA step is most flexible, while the GG(CC) step is least flexible. The flexibility of roll is quite anisotropic; the ratio of fluctuations toward the major and minor grooves is the largest for the GC step and the smallest for the AA(TT) and CG steps. Propeller twisting of base pairs is quite flexible, especially of A.T base pairs; propeller twist can reach 19 degrees by thermal fluctuation. We discuss the effect of electrostatic parameters, comparison with available experimental results, and biological relevance of these results.     

Distinct patterns in homooligomer tract sequence context in prokaryotic and eukaryotic DNA

The distributions of the junction sequences of homooligomer tracts of various lengths have been examined in prokaryotic DNA sequences and compared with those of eukaryotes. The general trends in the nearest and next to nearest neighbors to the tracts are similar for both groups. In both prokaryotes and eukaryotes A/T runs are preferentially flanked on either the 5' or the 3' ends by A and/or T. G/C runs are preferentially flanked by G and/or C. There is discrimination against A/T runs flanked by G or C and G/C runs flanked by A or T. However, whereas the distribution of prokaryotic homooligomer tract junction sequences was quite homogeneous, large variations were observed in the 5-fold larger eukaryotic database, increasing in magnitude from tracts of length 2 to 3 to 4 base pairs long. Possible DNA conformational implications and in particular DNA curvature and packaging aspects of prokaryotes and eukaryotes are discussed.     

Molecular species of platelet-activating factor generated by human neutrophils challenged with ionophore A23187

Two species of platelet-activating factor (PAF), 1-hexadecyl- and 1-octadecyl-2-acetyl-sn-glycero-3-phosphocholine (C16 = 0 AGEPC and C18 = 0 AGEPC) were detected in ionophore A23187-stimulated human neutrophils. The amount of AGEPC in 1 x 10(7) neutrophil cells was 80 +/- 26 pmol (mean +/- standard error) with a range of 14 to 223 pmol (n = 8), and it consisted of 80% of the C16 = 0 species and 20% of the C18 = 0 species. Most of the AGEPC derived from ionophore-treated neutrophils remained cell associated rather than being secreted into the medium, even when the medium contained ample albumin protein, which can trap AGEPC. These results were obtained by a technique of gas chromatography-mass spectrometry coupled with selected ion monitoring.     

Production of platelet-activating factor by washed rabbit platelets

Production of platelet-activating factor by washed rabbit platelets under stimulation with the ionophore A23187 was investigated utilizing two groups of platelet preparations. The first platelet preparation contained 0.03 +/- 0.02% contaminating white cells, while the second preparation contained 0.48 +/- 0.27% white cells. The latter preparation produced platelet-activating factor, mainly 1-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine, 8.3 +/- 6.3 pmol (mean +/- standard deviation) with a range of 2.6 to 21.4 pmol (n = 9), followed by small quantities of 1-octadecenyl- and 1-octadecyl-2-acetyl-sn-glycero-3-phosphocholine. In contrast, there was no production of 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine by the former platelet preparation having 0.03% leukocytes. These quantitative analyses were carried out by the selected ion monitoring technique and it was concluded that it is necessary to consider the presence of contaminating white cells in studies on the production of platelet-activating factor by platelets.     

Amino acid sequence of polypeptide chain IIB of extracellular hemoglobin from the polychaete Tylorrhynchus heterochaetus

The giant extracellular hemoglobin from the polychaete Tylorrhynchus heterochaetus consists of two types of subunits: a "monomeric" chain (chain I) and a disulfide-bonded trimer of chains IIA, IIB, and IIC. The complete amino acid sequence of chain IIB was determined. This chain has 148 amino acid residues and a molecular weight of 17,236 including a heme group. Of the residues in chain IIB, 74 (50%) and 34 (30%) were found to be identical with those in the corresponding positions in Tylorrhynchus chains IIC and I, respectively (Suzuki, T., Furukohri, T., and Gotoh, T. (1985) J. Biol. Chem. 260, 3145-3154). Marked differences were found between the chains of Tylorrhynchus and Lumbricus in the COOH-terminal regions. Significant differences were predicted between the monomeric chain I and the "trimeric" chains (IIB and IIC) in the hydropathy profiles and alpha-helical contents.     

Glutelin accumulation and changes in the levels of its mRNA in the superior and inferior spikelets of rice ear during ripening

Glutelin accumulation in the apical spikelet of the top primary branch (superior spikelet) and the second spikelet of the lowest secondary branch (inferior spikelet) of the ear of the rice plant (Oryza sativa L.) was characterized during grain filling.In the superior spikelet, the accumulation of dry matter and nitrogen started immediately after flowering and rapidly reached the maturation level by 20 days after heading (DAH). At 7 DAH, total RNA content had already reached its maximum level and glutelin mRNA content 70% of its maximum. The increase in glutelin mRNA was followed by a rapid increase in glutelin between 7 and 16 DAH.In the inferior spikelet dry matter, nitrogen and glutelin accumulation were low immediately after flowering and increased only after grain filling of the superior spikelet was almost complete. Total RNA and glutelin mRNA increased much later at slower rates than in the superior spikelet.It is very likely that the retardation of dry matter, total nitrogen and glutelin accumulation in the inferior spikelet is due to retardation of differentiation and development of endosperm tissue, and to glutelin gene expression in endosperm cells. It is suggested that the delayed development resulted from limited partitioning of nutrients to the inferior spikelet at the early stage of ripening.     

Determination of the NMR solution structure of a specific DNA complex of the Myb DNA-binding domain

Summary The solution structure of a specific DNA complex of the minimum DNA-binding domain of the mouse c-Myb protein was determined by distance geometry calculations using a set of 1732 nuclear Overhauser enhancement (NOE) distance restraints. In order to determine the complex structure independent of the initial guess, we have developed two different procedures for the docking calculation using simulated annealing in four-dimensional space (4D-SA). One is a multiple-step procedure, where the protein and the DNA were first constructed independently by 4D-SA using only the individual intramolecular NOE distance restraints. Here, the initial structure of the protein was a random coil and that of the DNA was a typical B-form duplex. Then, as the starting structure for the next docking procedure, the converged protein and DNA structures were placed in random molecular orientations, separated by 50 Å. The two molecules were docked by 4D-SA utilizing all the restraints, including the additional 66 intermolecular distance restraints. The second procedure comprised a single step, in which a random-coil protein and a typical B-form DNA duplex were first placed 70 Å from each other. Then, using all the intramolecular and intermolecular NOE distance restraints, the complex structure was constructed by 4D-SA. Both procedures yielded the converged complex structures with similar quality and structural divergence, but the multiple-step procedure has much better convergence power than the single-step procedure. A model study of the two procedures was performed to confirm the structural quality, depending upon the number of intermolecular distance restraints, using the X-ray structure of the engrailed homeodomain-DNA complex.Abbreviations rmsd root-mean-square deviation - NOE nuclear Overhauser enhancement - 4D-SA simulated annealing in four-dimensional space - Myb-R2R3 repeats 2 and 3 of the DNA-binding domain of the c-Myb protein - DNA 16 Myb-specific binding DNA duplex with 16 base pairs - IHDD-C residues 3 to 59 of the C-chain of the engrailed homeodomain-DNA complex - DNA11 DNA duplex with base pairs 9 to 19 of the engrailed homeodomain-DNA complex     

Linkage of Mercury, Cadmium, and Arsenate and Drug Resistance in Clinical Isolates of Pseudomonas aeruginosa

Of the 787 isolates, 99.8% were metal resistant, with most (99.5%) showing multiple resistance. Fifty-three percent of the isolates were both metal and drug resistant, whereas only 19% were metal resistant and drug sensitive.