Ultrafiltration of protein solutions; the role of protein association in rejection and osmotic pressure

The monomer-dimer equilibrium of the protein β-lactoglobulin under neutral conditions appears to influence the rejection and the osmotic pressure build-up, both phenomena closely related to ultrafiltration. Rejection measurements indicate different rejections for the β-lactoglobulin monomers and dimers: the membrane rejects the dimer almost completely and the monomer only partially. The osmotic pressure turns out to be highly dependent on the protein concentration. A good agreement, up to high concentrations, is found between experimental data and theoretical osmotic pressures, calculated by taking into account the state of association, the excluded volume and the Donnan effects. The effect of changes in pH on the osmotic pressure has been measured: a minimum was found around pH = 4.5, where according to the literature, maximum protein-protein interaction occurs

Characterization of clean and fouled ultrafiltration membranes

Much research into the fundamentals of membrane formation and separation has been performed in order to improve the efficiency of the manufacture of ultrafiltration membranes. Determination of the membrane characteristics is a key problem in these investigations. In this paper, we report on a study of membrane morphology by fractional rejection measurements, using low molecular weight saccharides as the test solute, and by electron microscopy. Using a simple model for solute/solvent transport through cylindrical pores, a “characteristic pore size” was derived from saccharide rejection data. This pore size of a hypothetical isoporous membrane, interpreting the measured separation characteristics, provides a promising means of describing differences between membranes with respect to pore size and pore size changes caused by solute adsorption. From high resolution electron micrographs, information was obtained on the skin layer morphologies and, for some membranes the sizes of the larger pores could be estimated

Terrace Standard, February, 09, 2000

Background. Loss of vessel wall integrity by degradation is essential for the development of abdominal aortic aneurysm (AAA) and ultimately its rupture. The observed greater rupture rate in women with AAA might be related to gender differences in the biomechanical properties of the aneurysm wall. The aim of the study was to compare the biomechanically important structure of collagen between men and women with AAA. Methods. Biopsies of the aneurysm walls were obtained during elective open repair of men (n = 14) and women (n = 14) treated for AAA. High-performance liquid chromatography (HPLC), Western blot, messenger RNA expression, and histochemical analyses were performed to assess the cross-linking and the amount and the composition of collagen. Results. There was neither a difference in the thickness of the aneurysm wall, nor in the histological evaluation of the collagen composition between the sexes. Relative collagen content in the aneurysm wall was similar in men and women, as assessed by messenger RNA expression and HPLC. Collagen cross-linking differed between the sexes; women had more lysyl pyridinoline (LP) than men (0.140 vs 0.07; P = .005), resulting in a lower hydroxyl pyridinoline (HP):LP ratio (3.28 vs 8.41; P = .003). There was no difference in messenger RNA and protein expressions of lysyl hydroxylase and lysyl oxidase to associate with the lower HP:LP ratio in women. Conclusions. The composition of collagen in the aneurysm wall of men and women are in several aspects similar, with the exception of collagen cross-linking, suggesting that the difference in rupture rate between the sexes rather depend on the composition of other vessel wall structures. Clinical Relevance The marked differences in prevalence and rupture risk of abdominal aortic aneurysm between men and women suggest gender to be of importance for both aneurysm development and progression. To study the amount and composition of collagen in men and women is of great importance for the understanding of the degenerative process occurring in aneurysms in both sexes and how it potentially differs, in regards to the increased rupture rate observed in women

Memstill® - Low cost membrane distillation technology for seawater desalination

Despite widespread research and development efforts during the last 25 years, membrane distillation still is not an accepted process for seawater desalination. A consortium of nine parties is presently developing a modified air gap membrane distillation (AGMD) process, aiming at presenting a low-cost alternative for both large and small scale RO, MSF and MED. This Memstill® process is designed in such a way that problems met so far in MD developments: high heat consumption and heat loss, low flux, expensive membranes, susceptibility to pore wetting and fouling - for the most part are solved. Various aspects of the process will be discussed, including system design, thermodynamic and mass and heat transfer aspects, trials with regard to pore wetting, bench scale results, North Sea water, outlook for the process. © 2004 Elsevier B.V. All rights reserved

A novel and simple immunocapture assay for determination of gelatinase-B (MMP-9) activities in biological fluids : Saliva from patients with Sjögren's syndrome contain increased latent and active gelatinase-B levels

Here we describe a new principle for accessing the activity of the different members of the human matrix-metalloproteinases (MMPs) by a colorimetric assay. Using protein engineering, a modified pro-urokinase was made in which the activation sequence, normally recognized by plasmin (ProArgPheLys ↓ IlelleGlyGly), was replaced by a sequence that is specifically recognized by MMPs (ArgProLeuGly ↓ IleIleGlyGly). The active urokinase resulting from the activation of this modified pro-urokinase by MMPs can be measured directly using a chromogenic peptide substrate for urokinase. The assay has been made specific for MMP-9 using an MMP-9 specific monoclonal antibody. Using this antibody MMP-9 is captured from biological fluids or tissue culture media, and MMP-activity of both active and latent MMP-9 can be analysed. We determined the gelatinase-B (MMP-9) activity present in saliva from patients with Sjögren's syndrome. Using a general gelatinase assay with radioactively-labeled gelatinated collagen it was observed that gelatinase activity was slightly, though not significantly, increased in patients: general gelatinase activity in patients versus healthy controls: 17.0 ± 4.9 vs 12.2 ± 2.5 x 104 cpm/ml (p > 0.05, and 44.0 ( 4.0 vs 36.1 ± 1.9 x 104 cpm/ml (p > 0.05), for active and latent gelatinase, respectively. However, using the immunocapture activity assay (using modified urokinase) specifically MMP-9 activity was measured, which was significantly increased in saliva from patients compared to healthy controls: MMP-9 (already active): patients 8.9 ± 2.5 U/mg, controls 1.0 ± 0.5 U/mg (p = 0.002); latent plus active MMP-9: patients 53.1 ± 9.8 U/mg, controls 16.5 ± 2.6 U/mg (p = 0.01). This assay, measuring MMP-9 activity using modified pro-urokinase as a substrate can easily be adapted for the specific detection of the various members of the MMP-family or other difficult to measure proteases, in a format that can be used for high throughput screening of compounds or samples

MMP-9 and MMP-2 activities in stomach and breast tumours, as measured by a novel MMP activity assay using modified urokinase as a substrate

Matrix metalloproteinases (MMPs) play an important role in many pathological processes. However, MMP activities are difficult to determine since no simple specific and/or chromogenic substrates exist. Therefore, we have developed a novel MMP activity assay using a modified urokinase as a substrate. In this urokinase, as obtained by protein engineering, the plasmin activation site was substituted by an activation site which is only specifically recognized by MMPs. In this way the MMP activity can be monitored via urokinase activity as measured by a simple chromogenic assay. The assay was made specific for either MMP-2 or MMP-9 by a catching step using specific MMP-2 or MMP-9 antibodies that do not interfere with MMP-activity. Both active (directly) and latent MMP (after activation with APMA) can be monitored. Using these assays it was observed that tissue homogenates contained hardly any active MMP-9. However, after activation by APMA tumor tissue homogenates from the stomach contained a higher MMP-9 activity compared to healthy tissue from the stomach. MMP-2 activity was hardly detectable in both tumor and normal tissue. In tissue homogenates from malign and benign breast tumours it was observed that homogenates from malignant tissue contained significantly more MMP-9, both in active and latent form. No differences were observed for MMP-2. These results suggest that in breast and stomach tumors MMP-9, but not MMP-2, might play an important role in tumour pathology

Membrane distillation against a pressure difference

Membrane distillation is an attractive technology for production of fresh water from seawater. The MemPower® concept, studied in this work, uses available heat (86 °C) to produce pressurized water (2.2 bar and 46 °C) by membrane distillation, which again can be used to power a turbine for co-production of electricity. We develop a non-equilibrium thermodynamic model to accurately describe the transfer at the liquid-membrane interfaces, as well as through the hydrophobic membrane. The model can explain the observed mass flux, and shows that 85% of the energy is dissipated at the membrane-permeate interface. It appears that the system's performance will benefit from a lower interface resistance to heat transfer, in particular at the permeate side of the membrane. The nature of the membrane polymer and the pore diameter may play a role in this context

In situ phenol removal from fed-batch fermentations of solvent tolerant Pseudomonas putida S12 by pertraction

In situ phenol pertraction with 1-octanol has been experimentally studied to improve the production of the model component phenol by a recombinant strain of Pseudomonas putida S12. When the phenol concentration in the reactor reaches 2mM, the cells in fermentations without phenol removal are inhibited in growth and phenol production. Growth and phenol production stop after approximately 80h at a phenol concentration in the reactor of 3.8mM. When phenol is removed from the fermentation broth by pertraction, a lower maximum aqueous phenol concentration of 2.6mM is achieved, while the total phenol production increases to 132%, as compared to the fermentation without pertraction. There are indications that the volumetric productivity (mmolL-1h-1) increases slightly in the fermentations with in situ pertraction compared to the reference experiments. As expected, the amount of phenol produced per gram biomass (the specific productivity, mmolg-1L-1) remains constant in time for all fermentations. The use of pertraction for in situ phenol removal is compared to in situ second phase extraction, in situ solvent impregnated resins and in-stream pertraction. Although the system shows promising results, further modifications such as using a solvent with a higher partition coefficient can improve the overall performance. © 2010 Elsevier B.V