PubMed · 8972481
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Q Al-Awqati. 1996. Puzzling polycystin.. https://pubmed.ncbi.nlm.nih.gov/8972481/
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Protein tyrosine phosphorylation cascades are difficult to analyze and are critical for cell signaling in higher eukaryotes. Methodology for profiling tyrosine phosphorylation, considered herein as the assignment of multiple protein tyrosine phosphorylation sites in single analyses, was reported recently (Salomon, A. R.; Ficarro, S. B.; Brill, L. M.; Brinker, A.; Phung, Q. T.; Ericson, C.; Sauer, K.; Brock, A.; Horn, D. M.; Schultz, P. G.; Peters, E. C. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 443-448). The technology platform included the use of immunoprecipitation, immobilized metal affinity chromatography (IMAC), liquid chromatography, and tandem mass spectrometry. In the present report, we show that when using complex mixtures of peptides from human cells, methylation improved the selectivity of IMAC for phosphopeptides and eliminated the acidic bias that occurred with unmethylated peptides. The IMAC procedure was significantly improved by desalting methylated peptides, followed by gradient elution of the peptides to a larger IMAC column. These improvements resulted in assignment of approximately 3-fold more tyrosine phosphorylation sites, from human cell lysates, than the previous methodology. Nearly 70 tyrosine-phosphorylated peptides from proteins in human T cells were assigned in single analyses. These proteins had unknown functions or were associated with a plethora of fundamental cellular processes. This robust technology platform should be broadly applicable to profiling the dynamics of tyrosine phosphorylation.
Isolation of recombinant protein drugs from cell culture supernatant is usually performed in batch mode, even if the fermentation process itself is continuous. As a novel approach, continuous separation techniques like continuous annular chromatography (CAC) can be used for continuous isolation. The potential of CAC for industrial application is demonstrated by continuous isolation of rFVIII from cell culture supernatant in pilot scale (i.e., 144-288 l/day). Thirty-fold concentration can be achieved at 94% yield, while purity is increased 3-5-fold. For this a batch direct feed ion exchange chromatography method was adapted to a commercial preparative CAC system (P-CAC). A headspace loading technique was used to maximize the concentration factor, while buffer incompatibility problems were addressed by a specifically modified inlet geometry. To allow sterile on-line coupling to FVIII-producing perfusion fermenters, an autoclavable pilot scale P-CAC prototype was developed. General characterization of P-CAC revealed a current limitation of the technology, i.e., variations in the outlet flow rates of up to +/-20%. These flow variations are shown to be caused mainly by a nonuniform annular resin bed and in turn result in "peak wobbling," i.e., the slight variation of peak position (up to +/-4 degrees ) and shape (e.g., A(s) = 0.9-1.4) as a specific function of column position. Some additional peak broadening, although less significant, is caused by a "peak oscillation" effect that results from the necessary segmentation of flow into discrete outlets. Both effects are only measurable if peaks are either monitored continuously or at least measured at multiple column positions. For isolation processes, these nonideal flow phenomena mean that more outlet streams have to be collected in order to achieve maximum yield and thus the achievable concentration factor is somewhat lower than the theoretical maximum.
The fabrication and surface modification of a porous cell scaffold are very important in tissue engineering. Of most concern are high-density cell seeding, nutrient and oxygen supply, and cell affinity. In the present study, poly(L-lactic acid) and poly(L-lactic-co-glycolic acid) (70/30) cell scaffolds with different pore structures were fabricated. An improved method based on Archimedes' Principle for measuring the porosity of scaffolds, using a density bottle, was developed. Anhydrous ammonia plasma treatment was used to modify surface properties to improve the cell affinity of the scaffolds. The results show that hydrophilicity and surface energy were improved. The polar N-containing groups and positive charged groups also were incorporated into the sample surface. A low-temperature treatment was used to maintain the plasma-modified surface properties effectively. It would do help to the further application of plasma treatment technique. Cell culture results showed that pores smaller than 160 microm are suitable for human skin fibroblast cell growth. Cell seeding efficiency was maintained at above 99%, which is better than the efficiency achieved with the common method of prewetting by ethanol. The plasma-treatment method also helped to resolve the problem of cell loss during cell seeding, and the negative effects of the ethanol trace on cell culture were avoided. The results suggest that anhydrous ammonia plasma treatment enhances the cell affinity of porous scaffolds. Mass transport issues also have been considered.