Enhancement of protein precipitate strength and density by low-frequency conditioning

The use of a continuous, low-frequency conditioning process to alter the structure of protein precipitate aggregates is examined. An increase in the density of aggregates is correlated with the levels of fluid acceleration and hence hydrodynamic stress to which the aggregates are exposed during conditioning. A combination of low-frequency conditioning followed by shear break-up (as in the feed zone to a high-speed disk-stack centrifuge) is shown to result in a precipitate suspension of increased particle size at the fine end of the distribution, and having a greater sedimentation velocity. The resistance of large aggregates to shear disruption is increased by low-frequency conditioning.List of Symbols CR conditioning ratio - CRS conditioning ratio after shearing - d m amplitude of displacement - D m particle size - D _c m critical size for centrifuge recovery - f s^–1 frequency of vibration - G s^–1 mean velocity gradient - Q m³/s volumetric throughput - SR shear ratio - t s ageing time Greek Symbols s^–1 mass-average shear rate - K sedimentation shape factor - _a kg/m³ aggregate density - _f kg/m³ fluid density - _s kg/m³ solids density - kg/m³ aggregate-suspension density difference - Ns/m² kinematic viscosity - amplitude of pulse ratio (ref. 23, 9) - s mean residence time - _s solids volume fraction     

Assignment of the backbone 1H and 15N NMR resonances of bacteriophage T4 lysozyme

The proton and nitrogen (15NH-H alpha-H beta) resonances of bacteriophage T4 lysozyme were assigned by 15N-aided 1H NMR. The assignments were directed from the backbone amide 1H-15N nuclei, with the heteronuclear single-multiple-quantum coherence (HSMQC) spectrum of uniformly 15N enriched protein serving as the master template for this work. The main-chain amide 1H-15N resonances and H alpha resonances were resolved and classified into 18 amino acid types by using HMQC and 15N-edited COSY measurements, respectively, of T4 lysozymes selectively enriched with one or more of alpha-15N-labeled Ala, Arg, Asn, Asp, Gly, Gln, Glu, Ile, Leu, Lys, Met, Phe, Ser, Thr, Trp, Tyr, or Val. The heteronuclear spectra were complemented by proton DQF-COSY and TOCSY spectra of unlabeled protein in H2O and D2O buffers, from which the H beta resonances of many residues were identified. The NOE cross peaks to almost every amide proton were resolved in 15N-edited NOESY spectra of the selectively 15N enriched protein samples. Residue specific assignments were determined by using NOE connectivities between protons in the 15NH-H alpha-H beta spin systems of known amino acid type. Additional assignments of the aromatic proton resonances were obtained from 1H NMR spectra of unlabeled and selectively deuterated protein samples. The secondary structure of T4 lysozyme indicated from a qualitative analysis of the NOESY data is consistent with the crystallographic model of the protein.     

Autonomic nervous control of gastric somatostatin secretion from the perfused rat stomach

The effect of parasympathetic and sympathetic nerve stimulation on the secretion of gastric somatostatin and gastrin has been studied in an isolated perfused rat stomach preparation. Stimulation of the vagus nerve inhibited somatostatin secretion and increased gastrin release. Splanchnic nerve stimulation increased somatostatin release during simultaneous atropine perfusion, but not in its absence, whereas gastrin secretion was unchanged. The secretory activity of the gastric D-cell was therefore reciprocally influenced by the sympathetic and parasympathetic nerves but sympathetic stimulation was only effective during muscarinic blockade.     

Effects of n-alkanes on the morphology of lipid bilayers A freeze-fracture and negative stain analysis

The effect of $\text{n-}\text{alkanes}$ on the ultrastructure of lipid bilayers has been investigated using freeze-fracture and negative stain electron microscopy. It has been found that the morphology of bilayers containing the long alkane tetradecane is quite different from bilayers containing the short alkane hexane. The smooth fracture faces of gel and liquid crystalline state bilayers are unmodified by tetradecane. However, hexane dramatically alters the hydrophobic bilayer interior, producing large (20 to 50 nm) mounds and depressions in the fracture faces. The fracture steps in these multilayer preparations containing hexane are variable in thickness and often considerably wider than the corresponding fracture steps in multilayers which contain tetradecane or are solvent-free. Alkanes also modify the structure of the P_β′ or ‘banded’ phase of phosphatidylcholine bilayers. The incorporation of tetradecane removes the banded structure from both the bilayer's hydrophilic surface, as viewed by negative staining, and the bilayer's hydrophobic interior, as viewed by the freeze-fracture technique. These results are consistent with X-ray diffraction data which imply that long alkanes are primarily located between adjacent lipid hydrocarbon chains in each monolayer of the bilayer, while short alkanes can partition into the geometric center of the bilayer between apposing monolayers.     

Tightly bound calcium of adenosine triphosphatase in sarcoplasmic reticulum from rabbit skeletal muscle

Sarcoplasmic reticulum vesicles were shown to possess a class of tightly bound calcium ions, inaccessible to the chelator, ethylene glycol bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid at 0 degrees C or 25 degrees C, amounting to 4.5 nmol/mg of protein (approximately 0.5 mol/mol (Ca2+,Mg2+)-ATPase). The calcium ionophores, A23187 and X537A, induced rapid exchange of tightly bound calcium in the presence of chelator. Chelator alone at 37 degrees C, caused irreversible loss of bound calcium, which correlated with uncoupling of transport from (Ca2+,Mg2+)-ATPase activity. Uncoupling was not accompanied by increased permeability to [14C]inulin. Slow exchange of tightly bound calcium with medium calcium was unaffected by turnover of the ATPase or by tryptic cleavage into 55,000- and 45,000-dalton fragments. Binding studies with labeled calcium suggested that tight binding involves a two-step process: Ca2+ + E in equilibrium K E . Ca2+ leads to E < Ca2+ where E and < Ca2+ represent the ATPase and tightly bound calcium, and K = 1.6 X 10(3) M-1. It is suggested that tightly bound calcium is located in a hydrophobic pocket in, or in close proximity to the ATPase, and, together with tightly bound adenine nucleotides (Aderem, A., McIntosh, D. B., and Berman, M. C. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 3622-03632), is related to the ability of the ATPase to couple hydrolysis of ATP to vectorial transfer of calcium across the membrane.     

Effect of benzyl alcohol on lipid bilayers. A comparisons of bilayer systems.

The effect of the small anesthetic molecule, benzyl alcohol, on the structure of various bilayer system has been studied by optical, electrical, and x-ray diffraction techniques. We find that the modifications in bilayer thickness caused by benzyl alcohol differ dramatically for planar (or black lipid) bilayers containing solvent, planar bilayers containing little or no solvent, and vesicular bilayers. Benzyl alcohol increases the thickness of planar bilayers containing n-alkane solvents, yet decreases the thickness of "solvent-free" planar bilayers. The effect of benzyl alcohol on vesicular bilayers below the phase transition temperature also depends on whether solvent is present in the bilayers. Without solvent, gel-state bilayers are reduced in thickness by benzyl alcohol, whereas in the presence of solvent, the thickness is unchanged. Above the phase transition temperature, benzyl alcohol has no measurable effect on vesicular bilayer thickness, whether solvent is present or not. These results indicate that different model membrane systems respond quite differently to a particular anesthetic.     

Changes in phosphorus concentrations in a eutrophic lake as a result of macrophyte-kill following herbicide application

Phosphorus (P) concentrations in water and sediment of a highly eutrophic lake were monitored before and after application of diquat to control the macrophyte Potamogeton crispus. Only a relatively small and short-term increase in P concentration in water occurred shortly after plant die-off resulting from herbicide application. Phosphorus concentrations in shallow water sediments decreased during the summer, and those in deep water sediments increased. Although a large increase in P concentration in the water occurred in late summer, it was not attributed to diquat. No major secondary effects of herbicide application were found during this study.     

Effects of condensed phosphates on plant growth and phosphorus uptake

Summary Four condensed phosphates with large and small molecules, including ring and chain structures, were equivalent to orthophosphate in terms of phosphorus uptake and the dry matter yield of ryegrass grown in two soils in pots. This equivalence was maintained at each of 6 cuts during two seasons.Increasing N rate greatly increased uptake of applied phosphorus but there was no differential effect with different sources of phosphorus, nor was there any interaction between source and application rate.Phosphorus was not leached at any time, indicating that the phosphates were rapidly adsorbed by the soils.Fairly rapid hydrolysis of all the condensed phosphates occurred in a soil of neutral pH but a slower hydrolysis seemed to occur in an acid soil.There was a good correlation between the phosphorus uptake by ryegrass and the additional orthophosphate released by an acid hydrolysis of soil extracts.