PubMed · 4931101
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R R Crichton. 1971-06-24. Ferritin: structure, synthesis and function.. https://doi.org/10.1056/nejm197106242842506
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Amino acid (AA) profiles from body fluids such as blood and urine are clinical indicators for diagnosing metabolic and hepatic diseases. Current quantitative methods, such as liquid chromatography-mass spectrometry (LC-MS) with isotopically labelled internal standards (ISs), are costly and technically demanding. This study proposes a cost-efficient alternative using structural isomers as ISs in a direct liquid infusion (DLI) tandem mass spectrometry (MS/MS) approach. The method leverages chimeric spectra and fragment intensity ratios to quantify AAs, demonstrating high linearity and precision even with a 3D ion trap mass analyser. This approach offers a viable strategy for AA quantification in preventive medicine, particularly for screening metabolic diseases such as phenylketonuria, diabetes, and liver dysfunction.
Glycosyl-phosphatidylinositol-anchored hydrophobic placental folate receptors (PFRs), which have an important functional role in maternal-to-fetal transplacental folate transport, can be converted to soluble hydrophilic forms by a placental metalloprotease. Using a Triton X-114 temperature-induced phase separation assay to monitor enzyme-mediated conversion of radiolabeled hydrophobic PFR into hydrophilic PFR, a metalloenzyme was isolated to apparent homogeneity from Triton X-114-solubilized human placenta using concanavalin A-Sepharose and reverse-phase high performance liquid chromatography (HPLC) as major purification steps. The purified hydrophobic enzyme eluted as a single protein peak on reverse-phase HPLC and SDS-polyacrylamide gel electrophoresis revealed a single 63,000 M(r) species, which was reduced to 58,000 M(r) following deglycosylation, findings comparable with amino acid analysis (M(r) approximately 59,000). The metalloenzyme was activated by Mg2+, Zn2+, Mn2+, and Ca2+, optimally at physiologic pH; it also exhibited EDTA-sensitive endoproteolytic cleavage of [3H]leucine-labeled full-length nascent PFR polypeptide generated in vitro in the absence of microsomes. Rabbit polyclonal anti-metalloprotease antiserum specifically immunoprecipitated 125I-metalloprotease and recognized cross-reacting moieties on plasma membranes of normal human hematopoietic progenitor cells and human cervical carcinoma cells, both of which also express FR.
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