Alpha 1-microglobulin: clinical laboratory aspects and applications

Penders, Joris; Delanghe, Joris

doi:10.1016/j.cccn.2004.03.037

Cited by 113 publications

(61 citation statements)

References 103 publications

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“…The aggregate concentration in plasma of globulins with a molecular size similar to albumin, proteins such as transferrin, ␣ 1 -acid glycoprotein, ␣ 1 -proteinase inhibitor, ␣ 1 -antichymotrypsin, ␣ 2 -HS glycoprotein, hemopexin, Gc-globulin, and many others (31 ), in healthy individuals is ϳ25% that of albumin; this aggregate concentration is even higher during acutephase reactions (32 ). Because the passage of plasma proteins through the glomerular barrier into urine is primarily a size-dependent process with a size-exclusion limit approximately the size of albumin (33 ), it is not surprising that all of the albumin-sized plasma components are also found in urine (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(33)(34)(35)(36)(37)(38)(39). There is considerable variation in the reported proportions of individual globulins relative to albumin in urine (Table 3).…”

Section: Discussionmentioning

confidence: 99%

Coelution of Other Proteins with Albumin during Size-Exclusion HPLC: Implications for Analysis of Urinary Albumin

et al. 2006

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Background: Size-exclusion HPLC has been used as an alternative to immunoassays for quantifying urinary albumin (microalbumin). Systematically higher values for the HPLC method have been proposed to result from nonimmunoreactive albumin. Methods: We evaluated separation of purified proteins and urinary components by size-exclusion HPLC using a Zorbax Bio Series GF-250 column eluted with phosphate-buffered saline. Urinary components eluting in the "albumin" peak were analyzed by mass spectrometry and reversed-phase HPLC. Results: Several proteins, such as transferrin, ␣ 1 -proteinase inhibitor, ␣ 1 -acid glycoprotein, and ␣ 2 -HS glycoprotein, analyzed as purified components, were not resolved from albumin by size-exclusion HPLC. Peaks for other proteins, such as IgG and urinary components identified as dimers of ␣ 1 -microglobulin and immunoglobulin light chains, overlapped with the albumin peak. Profiles of urine specimens showed variable amounts of components overlapping with albumin. Furthermore, the albumin peak obtained by size-exclusion HPLC was found by mass spectrometry and reversedphase HPLC to contain multiple components in addition to albumin. Conclusions: Size-exclusion HPLC does not resolve albumin from several other proteins in urine. The albumin peak resolved by this technique, although predominantly composed of albumin, contains several coelut-

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Section: Discussionmentioning

confidence: 99%

Coelution of Other Proteins with Albumin during Size-Exclusion HPLC: Implications for Analysis of Urinary Albumin

et al. 2006

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“…Not all of the unpaired Cys residues in these proteins may be available for disulfide formation with thiol-containing amino acid, because some of these unpaired Cys residues, such as in apolipoprotein A-II, are observed to form disulfide-linked homodimers or heterodimers with other proteins (18,20,(22)(23)(24). A portion of IgA and prothrombin molecules form disulfide bonds with ␣ 1 -microglobulin (25 ). ␣ 1 -Acid glycoprotein may be one of the more abundant plasma proteins, besides albumin, with an unpaired Cys, but there are 2 genes encoding this protein, and only the gene 2 contains an unpaired Cys (26 ).…”

Section: Discussionmentioning

confidence: 99%

Bound Homocysteine, Cysteine, and Cysteinylglycine Distribution between Albumin and Globulins

2006

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Background: Major portions of homocysteine (Hcy), cysteine (Cys), cysteinylglycine (CysGly), and glutathione in serum are covalently bound to proteins via disulfides. Albumin has been considered the dominant binding protein. Methods:Pooled serum and plasma from healthy adults were fractionated into albumin and globulins by affinity columns. Content of Hcy, Cys, CysGly, and glutathione was determined for serum and plasma fractions and purified proteins by an HPLC method before and after incubation with excess CysGly, Hcy, or glutathione Results: Of protein-bound amino acids in pooled serum, 12% of Hcy, 21% of Cys, and 33% of CysGly were bound to globulins, with the remainder bound to albumin. Slightly higher proportions were bound to globulins in pooled plasma. Globulins had ϳ16% of total exchangeable disulfide and thiol groups in serum based on results of loading with CysGly. These results agree with expected abundance of unpaired Cys residues in globulins relative to albumin. Significant amounts of disulfide-linked amino acids were detected for HDL and ␣ 1 -acid glycoprotein but not for transferrin. Exchange of disulfide-linked amino acids on exposure to excess Hcy or glutathione was much faster for albumin than for ␣ 1 -acid glycoprotein.Conclusions: Approximately 10%-30%, of proteinbound Hcy, Cys, and CysGly are disulfide-linked to globulins. Amino acids disulfide-linked to albumin are rapidly exchangeable, while exchange of disulfidelinked amino acids from globulins, such as ␣ 1 -acid glycoprotein, is much slower. Consequently, the pools of Hcy, Cys, and CysGly bound to albumin and globulin

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“…In polypeptides with unpaired cysteine residues, such as subunits of transthyretin, apolipoprotein A-II, ␣ 1 -proteinase inhibitor, and albumin, disulfides may form with a variety of compounds, such as cysteine, cysteinylglycine, glutathione, or other polypeptides (dimerization of apolipoprotein A-II), or the sulfhydryl may undergo oxidation (19,20,28,(65)(66)(67). Proteins with unpaired cysteines also may link via disulfides to other proteins, as in the case of ␣ 1 -microglobulin, such that a mixture of different covalently bound forms of the protein is observed (68 ). Therefore, identification of unpaired cysteine residues is of major importance in establishing the masses and structural variations of proteins.…”

Section: Mass Assignments Of Plasma Componentsmentioning

confidence: 99%