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  • Measurement of human surfactant protein-B turnover in vivo from tracheal aspirates using targeted proteomics. 20178338

    We describe a method to measure protein synthesis and catabolism in humans without prior purification and use the method to measure the turnover of surfactant protein-B (SP-B). SP-B, a lung-specific, hydrophobic protein essential for fetal-neonatal respiratory transition, is present in only picomolar quantities in tracheal aspirate samples and difficult to isolate for dynamic turnover studies using traditional in vivo tracer techniques. Using infusion of [5,5,5-(2)H(3)] leucine and a targeted proteomics method, we measured both the quantity and kinetics of SP-B tryptic peptides in tracheal aspirate samples of symptomatic newborn infants. The fractional synthetic rate (FSR) of SP-B measured using the most abundant proteolytic fragment, a 10 amino acid peptide from the carboxy-terminus of proSP-B (SPTGEWLPR), from the circulating leucine pool was 0.035 +/- 0.005 h(-1), and the fractional catabolic rate was 0.044 +/- 0.003 h(-1). This technique permits high-throughput and sensitive measurement of turnover of low abundance proteins with minimal sample preparation.
    Document Type:
    Reference
    Product Catalog Number:
    Multiple
    Product Catalog Name:
    Multiple

  • Homocysteine and other thiols determined in plasma by HPLC and thiol-specific postcolumn derivatization. 8353942

    We describe a versatile high-performance liquid-chromatographic method for determining homocysteine and other plasma sulfhydryls. Using three different procedures for preparation of plasma, we determined total, free (non-protein-bound), and reduced forms of homocysteine, cysteine, glutathione, cysteinylglycine, and gamma-glutamylcysteine in human plasma. Sample preparation involves disulfide reduction with dithiothreitol and protein precipitation with sulfosalicylic acid. The assay utilizes isocratic reversed-phase ion-pair liquid chromatography at pH 2.4, postcolumn derivatization with 4,4'-dithiodipyridine, and colorimetric detection at 324 nm. The intra-assay precision (CV) of the method for total homocysteine is 1.5%; the interassay precision over 2.5 months is 2.5%. The detection limit for homocysteine is < 50 nmol/L plasma.
    Document Type:
    Reference
    Product Catalog Number:
    20-176
    Product Catalog Name:
    100X GTPγS, 10mM

  • Considerations when measuring urinary albumin: precision, substances that may interfere, and conditions for sample storage. 1764788

    The measurement of small but abnormal amounts of albumin in urine is important in evaluating kidney disease in people with diabetes mellitus, hypertension, or possible adverse health effects from exposure to nephrotoxins. Routine laboratory methods for measuring albumin are not sensitive enough to measure the amounts that are significant in urine (less than 30 mg/L). In our laboratory we used three immunoassays for measuring urinary albumin: enzyme-linked immunosorbent assay (EIA), radioimmunoassay (RIA), and immunoturbidimetric assay (IT). We calculated the CVs of the three methods, investigated potential interfering substances at three times their normal concentrations, and stored urine under different conditions to find the best way to protect the sample until assay. The potential interferents we checked were transferrin, urea, beta 2-microglobulin, retinol-binding protein, creatinine, kappa and lambda light chains, IgG, hemoglobin, ketone, and glucose. The stability study involved two study temperatures (-20 and -70 degrees C) and four treatments (centrifuging or filtering, before or after storage). We found the following: the RIA had the lowest CV; the results from the interference study showed no interference from normal physiological concentrations of the substances investigated; storage at -70 degrees C regardless of the treatment should be adequate to prevent loss of albumin immunoreactivity.
    Document Type:
    Reference
    Product Catalog Number:
    20-176
    Product Catalog Name:
    100X GTPγS, 10mM

  • Identification and quantification of Gi-type GTP-binding proteins that copurify with a pituitary somatostatin receptor 8449959

    Somatostatin (SRIF) receptors of GH4C1 cells occupied with biotinyl-NH-[Leu8,D-Trp22,Tyr25] somatostatin28 (bio-S28) have been affinity purified over streptavidin affinity columns (Eppler, C. M., Zysk, J. R., Corbett, M., and Shieh, H.-M. (1992) J. Biol. Chem. 267, 15603-15612). This procedure results in the copurification of a single subtype of SRIF receptor (SSTR2) and associated guanine nucleotide-binding proteins (G proteins) that are coupled to these receptors. For accurate quantification it was necessary to: (i) use homogenous recombinant standards; (ii) accurately assess the purity of standards; (iii) determine recovery of G proteins during sample preparation and Western blotting; and (iv) account for cross-reactivity among antisera. Four pertussis toxin-sensitive G proteins were quantified with previously characterized polyclonal antisera. Gi alpha 1 also was measured with a novel, more sensitive monoclonal antibody (7H7). Go alpha and Gi alpha 2 but not Gi alpha 1 and Gi alpha 3 were detected in membrane extracts prepared from GH4C1 cells. In contrast, the G proteins copurified with SSTR2 receptors were predominantly Gi alpha 2 (50% of total G protein) and Gi alpha 3 (36% of total G protein), whereas Go alpha and Gi alpha 1 were negligible. G beta subunits also were detected. Silver staining confirmed the absence of a 39-kDa protein, corresponding to the M(r) of Go alpha associated with purified SRIF receptor-G protein complexes. These data suggest that SRIF receptors selectively couple to two G proteins, one of which is sparsely expressed in GH4C1 cells; the data conform to the notion that SRIF receptors discriminate between similar pertussis toxin-sensitive G proteins.
    Document Type:
    Reference
    Product Catalog Number:
    Multiple
    Product Catalog Name:
    Multiple

  • Chromatin immunoprecipitation (ChIP): revisiting the efficacy of sample preparation, sonication, quantification of sheared DNA, and analysis via PCR. 22046253

    The "quantitative" ChIP, a tool commonly used to study protein-DNA interactions in cells and tissue, is a difficult assay often plagued with technical error. We present, herein, the process required to merge multiple protocols into a quick, reliable and easy method and an approach to accurately quantify ChIP DNA prior to performing PCR. We demonstrate that high intensity sonication for at least 30 min is required for full cellular disruption and maximum DNA recovery because ChIP lysis buffers fail to lyse formaldehyde-fixed cells. In addition, extracting ChIP DNA with chelex-100 yields samples that are too dilute for evaluation of shearing efficiency or quantification via nanospectrophotometry. However, DNA extracted from the Mock-ChIP supernatant via the phenol-chloroform-isoamyl alcohol (PCIA) method can be used to evaluate DNA shearing efficiency and used as the standard in a fluorescence-based microplate assay. This enabled accurate quantification of DNA in chelex-extracted ChIP samples and normalization to total DNA concentration prior to performing real-time PCR (rtPCR). Thus, a quick ChIP assay that can be completed in nine bench hours over two days has been validated along with a rapid, accurate and repeatable way to quantify ChIP DNA. The resulting rtPCR data more accurately depicts treatment effects on protein-DNA interactions of interest.
    Document Type:
    Reference
    Product Catalog Number:
    Multiple
    Product Catalog Name:
    Multiple
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