Bead-Extractor Assisted Ready-to-Use Reagent System (BEARS) for Immunoprecipitation Coupled to MALDI-MS.

Quantitative protein assays play an important role in the study of biological functions. Immunoassays and mass spectrometry are two main technologies for quantifying proteins in biological samples. The combination of immunoprecipitation (IP) with MALDI technology delivers high assay sensitivity and specificity, but the sample preparation procedure involves multiple washing and transfer steps. These steps can be performed either manually (requiring significant time and labor) or automatically (requiring the purchase of a complex liquid-handling workstation). This bottleneck has limited the widespread adoption of this technology. We present here the Bead-Extractor Assisted ready-to-use Reagent System (BEARS) technology for simplified, low cost protein and peptide immunoprecipitation combined with MALDI-MS detection. All of the reagents are stable during long-term storage and can be prepared in advance. In the BEARS technology, a magnetic-bead extractor is used to handle beads from 96 wells simultaneously. A BEARS-based method was developed for plasma renin activity (PRA) and was evaluated on fifty-three clinical samples. These experiments showed that the BEARS assay had an LOD and linear range comparable to the manual method and an automated iMALDI PRA assay, but was 4-times faster than the manual approach. The BEARS iMALDI results also correlated well with a conventional ELISA PRA assay, with a coefficient of determination of 0.98. The BEARS technology provides convenience and affordability, and extends the use of IP-based mass spectrometry technology to most research and clinical laboratories, including those in developing countries.

N-acetyl-L-tyrosine as a tyrosine source in adult parenteral nutrition.

BACKGROUND: N-acetyl-L-tyrosine (NAT) is commonly used in place of tyrosine in parenteral nutrition, but human studies carried out to date indicate considerable amounts of it are excreted unchanged in the urine. NAT retention has not been well studied in parenterally fed adults. METHODS: NAT retention was measured in 13 adults receiving continuous parenteral nutrition with Aminosyn II 15% (Abbott Laboratories, Abbott Park, IL). RESULTS: Approximately 35% of administered NAT was excreted unchanged in the urine, with no important effect of infusion rate, N balance, or level of renal function on this value. Sufficient NAT was retained that the prescription of 1 g total amino acids/kg x day(-1) using this product exceeded the combined recommended dietary allowance for aromatic amino acids CONCLUSION: As used in the clinical setting, the phenylalanine and NAT composition of Aminosyn II is sufficient to meet the combined aromatic amino acid needs of adults with normal phenylalanine hydroxylase activity.