Adsorption of ethylenediaminetetraacetic dianhydride modified oxalate decarboxylase on calcium oxalate

We used ethylenediaminetetraacetic acid dianhydride (EDTAD) to modify oxalate decarboxylase (OXDC) to improve its adsorption on calcium oxalate stones. The modified sites were identified by Ultra performance liquid chromatography-mass spectrometry (UPLC-MS) and the adsorption mechanism of the EDTAD-modified OXDC on calcium oxalate (CaOx) was investigated. We investigated adsorption time, initial enzyme concentration, temperature and solution pH on the adsorption process. Data were analyzed using kinetics, thermodynamics and isotherm adsorption models. UPLC-MS showed that EDTAD was attached to OXDC covalently and suggested that the chemical modification occurred at both the free amino of the side chain and the α-NH₂ of the peptide. The adsorption capacity of the EDTAD-OXDC on calcium oxalate was 53.37% greater than that of OXDC at the initial enzyme concentration of 5 mg/ml, pH = 7.0, at 37° C. The modified enzyme (EDTAD-OXDC) demonstrated improved oxalate degradation activity at pH 4.5?6.0. Kinetic data fitting analysis suggested a pseudo second order kinetic model. Estimates of the thermodynamic parameters including ΔG⁰, ΔH⁰ and ΔS⁰ of the adsorption process showed it to be feasible, spontaneous and endothermic. Isotherm data fitting analysis indicated that the adsorption process is reduced to monolayer adsorption at a low enzyme concentration and to multilayer adsorption at a high enzyme concentration. It may be possible to apply OXDC to degradation of calcium oxalate stones.     

Thermodynamic aspects of the gelatinization and swelling of crosslinked starch

Samples of epichlorohydrin crosslinked potato starch were prepared by using a high ratio of starch to water and alkali concentration below the gelatinization level. This yielded crosslinked samples that were partially crystalline, and where the number of crosslinks could be varied between 1 and 20 crosslinks per 100 anhydroglucose units. The degree of swelling varied regularly with degree of crosslinking, and the molecular weight between crosslinks M_c as derived from swelling data in a good swelling agent compared favorably with M_c derived from chemical analysis. From the heat of gelatinization of the crosslinked starches, as observed in a differential scanning calorimeter, for gelatinization in glycerol, water, and dimethylsulfoxide, a model for the gel state of the crosslinked starch is proposed. It is concluded that the entropy of melting is the determining factor in establishing the temperature of gelatinization.     

Mitochondrial DNA structure and colony expansion dynamics of New Zealand fur seals (Arctocephalus forsteri) around Banks Peninsula

New Zealand fur seals are one of many pinniped species that survived the commercial sealing of the eighteenth and nineteenth centuries in dangerously low numbers. After the enforcement of a series of protection measures in the early twentieth century, New Zealand fur seals began to recover from the brink of extinction. We examined the New Zealand fur seal populations of Banks Peninsula, South Island, New Zealand using the mitochondrial DNA control region. We identified a panmictic population structure around Banks Peninsula. The most abundant haplotype in the area showed a slight significant aggregated structure. The Horseshoe Bay colony showed the least number of shared haplotypes with other colonies, suggesting a different origin of re-colonisation of this specific colony. The effective population size of the New Zealand fur seal population at Banks Peninsula was estimated at approximately 2500 individuals. The exponential population growth rate parameter for the area was 35, which corresponds to an expanding population. In general, samples from adjacent colonies shared 4.4 haplotypes while samples collected from colonies separated by between five and eight bays shared 1.9 haplotypes. The genetic data support the spill-over dynamics of colony expansion already suggested for this species. Approximate Bayesian computations analysis suggests re-colonisation of the area from two main clades identified across New Zealand with a most likely admixture coefficient of 0.41 to form the Banks Peninsula population. Approximate Bayesian computations analysis estimated a founder population size of approximately 372 breeding individuals for the area, which then rapidly increased in size with successive waves of external recruitment. The population of fur seals in the area is probably in the late phase of maturity in the colony expansion dynamic.     

Effect of hydrocarbon concentration of pasture production (<i>Brachiaria humidicola</i>) in Texistepec,Veracruz

In this study, the relationship between the concentration of extra-heavy crude petroleum in a clayey material and the toxicity, field capacity, temperature, and growth of a tropical forage grass (Brachiara humidicola) was determined empirically. For this type of petroleum the acute toxicity (Microtox^®) was slight (CE₅₀ = 63200 - 76400 mg/kg) even at high hydrocarbon concentrations (29279 mg/kg). Nonetheless, serious impacts were encountered in terms of an increase in soil temperature (+ 1.3 °C), reduction in field capacity (-10.7%) and reduction in aerial biomass (-97%). The relationship between hydrocarbon concentration and biomass resulted in a typical dose-response curve (r = 0.99), where a concentration of 2626 mg/kg of hydrocarbons corresponds to a maintenance of 90% biomass. Furthermore, during the duration of this study (one year) the biodegradation was proportional to the pasture biomass production (r = 0.997) indicating a synergistic relationship between the petroleum biodegrading microorganisms in the rhizosphere and the pasture.     

In vitro chiral nematic ordering of chitin crystallites

Microfibrillar fragments of purified crab and shrimp chitin were prepared by hydrolysis in 3 HCl at its boiling point (104°C). After removal of the acid by centrifugal washing and dialysis, an ultrasound treatment converts the residual product to a colloidal suspension stabilized by NH₃⁺ charges. When dewatered to a critical concentration, spontaneous formation of a two-phase equilibrium system occurs. The upper phase (lower concentration) is isotropic and the lower phase is anisotropic. The latter displays chiral nematic order and dries to a solid film which mimics the helicoid organization characteristic of the chitin microfibrils in the cuticle of arthropods.     

Continuous Production of Long-Side-Chain Poly-β-Hydroxyalkanoates by Pseudomonas oleovorans

Shake flask experiments showed that Pseudomonas oleovorans began to be growth inhibited at 4.65 g of sodium octanoate liter^-1, with total inhibition at 6 g liter^-1. In chemostat studies with 2 g of ammonium sulfate and 8 g of octanoate liter^-1 in the feed, the maximum specific growth rate was 0.51 h^-1, and the maximum specific rate of poly-β-hydroxyalkanoate (PHA) production was 0.074 g of PHA g of cellular protein^-1 h^-1 at a dilution rate (D) of 0.25 h^-1. When the specific growth rate (μ) was <0.3 h^-1, the PHA composition was relatively constant with a C₄/C₆/C₈/C₁₀ ratio of 0.1:1.7:20.7:1.0. At μ > 0.3 h^-1, a decrease in the percentage of C₈ with a concomitant increase in C₁₀ monomers as μ increased was probably due to the effects of higher concentrations of unmetabolized octanoate in the fermentor. At D = 0.24 h^-1 and an increasing carbon/nitrogen ratio, the percentage of PHA in the biomass was constant at 13% (wt/wt), indicating that nitrogen limitation did not affect PHA accumulation. Under carbon-limited conditions, the yield of biomass from substrate was 0.76 g of biomass g of octanoate^-1 consumed, the yield of PHA was 0.085 g of PHA g of octanoate^-1 used, and 7.9 g of octanoate was consumed for each gram of NH₄⁺ supplied. The maintenance coefficient was 0.046 g of octanoate g of biomass^-1 h^-1. Replacement of sodium octanoate with octanoic acid appeared to result in transport-limited growth due to the water insolubility of the acid.     

Application of self-cycling fermentation technique to the production of poly-beta-hydroxybutyrate

The production of poly-beta-hydroxybutyrate (PHB) by Alcaligenes eutrophus DSM 545 in a cyclone bioreactor was compared using various culture methods: batch, fed-batch, and self-cycling fermentation (SCF) with and without extended periods of nutrient deprivation. SCF is a semi-continuous method that results in a nutrient limitation for every successive generation of cells and, therefore, may have advantages for products whose formation follow secondary metabolite kinetics. Use of the SCF technique without extended nutrient deprivation produced a PHB concentration of 1.2 g L(-1) as 40% of the biomass dry weight. With nitrogen deprivation for 4 or 6 h, the concentration of PHB decreased when compared to the standard SCF technique. However, nitrogen deprivation periods of 8 h resulted in an increase in PHB concentration to 2.7 g L(-1) or 59% of the biomass dry weight. The nutrient cycling may act to repress PHB accumulation during periods of nitrogen deprivation, unless a time threshold has been reached, after which PHB accumulation occurs as in normal batch culture. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 815-820, 1997.     

Structure of β,D(1–>4′)-xylan hydrate

A structure is proposed for xylan hydrate as a result of investigations by x-ray fiber diffraction and computer-aided chain-packing methods. The unit-cell dimensions are a = b = 9.16 Å, c (fiber axis) = 14.85Å, γ = 120° and the proposed anti-parallel chain arrangement corresponds to a space group symmetry of P3₂21. Left-handed threefold screw helices are stabilized in this conformation by their interaction with chains of water molecules, so that a satisfactory hydrogen-bonding scheme is achieved. The proposed structure provides an explanation of the changes in the x-ray diagram with relative humidity and yields a very good structure factors agreement. An x-ray fiber diagram corresponding to a higher hydrate (xylan dihydrate) is presented. Comments are made on the possible role of xylan in nature and in technological processes.