PubMed · 5978431
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A Dahlqvist. 1966-10-19. [Galactoseuria].. https://pubmed.ncbi.nlm.nih.gov/5978431/
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Despite the prominent role of IgA, particularly IgA1, in the pathogenesis of IgA nephropathy (IgAN), the precise role of this molecule in the process remains unclear. Four biotin-conjugated lectins in sandwich-type enzyme-linked immunosorbent assays were devised to determine the glycosylation profiles of total IgA and its subclasses. We took advantage of differential binding properties of these lectins to sugar residues to dissect the oligosaccharide chains O-linked to the hinge and those N-linked to the Fc region of total IgA and IgA subclasses in 47 patients with IgAN and an equal number of controls. The proportion of sialylated IgA1 was higher in patients compared with controls (p < 0.02), whereas IgA2 in patients appeared less well sialylated. A reduction of galactose in pathological IgA as detected by RCA-I became significant after treatment of the molecule with neuraminidase (p < 0.01). Defective galactosylation was also observed for patient IgA1 when it was probed with ECL, a lectin that has a specificity for Gal 1,4 N-acetylglucosamine groupings on N-linked oligosaccharides. The RCA and ECL results, therefore, suggest that increased sialylation on the IgA1 is on O-linked oligosaccharides in the hinge region. This was partly confirmed by a small increase in the binding of PNA to IgA1 from the patient group. This lectin binds preferentially to Gal 1,3 N-acetylgalactosamine groups that are found on O-linked oligosaccharides.
BACKGROUND/AIMS: An impaired methionine degradation along the transsulfuration pathway has been widely described in cirrhosis. Evidence has been provided that methionine can also be degraded via a transamination pathway, leading to formation of methanethiol and its metabolites, protein-S-SCH3 (a mixed disulphide of blood proteins and methanethiol), alpha-ketomethylthiobutyrate and X-S-SCH3 (a mixed disulphide of a thiol with an unknown component X and methanethiol). This pathway seems to be of little importance in normal subjects, even after methionine loading, but its role in the presence of an acquired transsulfuration defect has never been tested. METHODS: We measured the plasma concentration of methanethiol metabolites in six normal subjects and 11 patients with cirrhosis receiving a primed-continuous infusion of L-methionine, at rates able to increase plasma methionine to levels approximately 20 times basal concentrations. RESULTS: Before methionine infusion, the sum of transamination metabolites was similar in the two groups (0.29 +/- SD 0.07 mumol/l in controls and 0.45 +/- SD 0.22 in patients with cirrhosis). During methionine infusion and after the end of infusion, there was a progressive increase of transamination metabolites, which reached values approximately 10 times basal concentrations, with no difference between groups. CONCLUSIONS: We conclude that transamination cannot represent a quantitatively important exit for excess methionine in subjects with cirrhosis, in the presence of an acquired block along the transsulfuration pathway.
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