Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P00790 (PGA)
 2,475 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the presence of anti-insulin antibody, 2-to 3-fold enhancement of 125I-insulin binding to liver membranes was observed when binding was estimated by the radioactivity of 125I-insulin bound to the membrane pellets. However, after 125I-insulin was covalently cross-linked to liver membranes using disuccinimidyl suberate in the presence of anti-insulin antibody, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography showed that 125I-insulin bound to the alpha-subunit of the insulin receptor was inhibited by anti-insulin insulin antibody in an dose-dependent manner. More importantly, at an anti-insulin antibody dilution range between 1:50 and 1:5,000, sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed two 125I-labelled bands of mol wt 62,000 and 27,000, while only one band of mol wt 130,000 was revealed in the absence of anti-insulin antibody. These Mr = 62,000 and Mr = 27,000 bands were found to be the heavy and the light chain of anti-insulin IgG molecules respectively. Pepsin digested anti-insulin serum had only an inhibitory effect on 125I-insulin binding to liver membranes. Non-immunized guinea pig serum or IgG completely abolished the enhanced effect of anti-insulin antibody. Further, this enhanced effect was inhibited by Fc fragment-specific anti-IgG serum or H&L-chain-specific anti-IgG serum in a dose-dependent manner. Protein A also inhibited the effect of anti-insulin antibody. In IM-9 lymphocytes and human red blood cell ghosts, which have no Fc gamma receptors, enhancement of insulin binding was not observed in the presence of anti-insulin antibody.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of anti-insulin antibody on insulin binding to liver membranes: evidence against antibody-induced enhancement of insulin binding to the insulin receptor. 352 44

We asked whether binding of human immunoglobulin (Ig)G antibody reacting with Raji cells could be distinguished from binding of IgG immune complexes. Using a standard Raji assay employing 125I-IgG goat anti-human Fc gamma, we found that digestion of Raji cells with pronase reduced by 95% their ability to bind complement-fixed aggregated human gamma globulin and complement-fixed tetanus toxoid-antitetanus toxin complexes. However, binding at 37 degrees C of IgG from the sera of 16 patients with systemic lupus erythematosus (SLE) to pronase-digested Raji cells was reduced much less consistently and extensively (9-100% reduction; mean reduction of 51%). In more detailed studies of two SLE sera, sucrose density gradient centrifugation showed that greater than 50% of the IgG binding to undigested Raji cells sedimented in the 7S region. Pepsin digestion of immunoglobulin fractions from four SLE sera caused a reduction in SLE IgG binding to undigested Raji cells when detected with 125I anti-Fc gamma, but an increase when binding was detected with 125I-anti-Fab, suggesting that substantial SLE IgG can bind through F(ab')2 regions. Binding of IgG from SLE sera was not directed at neoantigenic sites induced by pronase digestion because binding activity was adsorbed with undigested cells as readily as with digested cells. Moreover, sera from 10 SLE patients that had negative Raji assays contained no IgG that bound to pronase-digested Raji cells. We conclude that much of the IgG bound at 37 degrees C to Raji cells from the sera of many patients with SLE does not represent immune complexes but is probably antibody directed toward sites on the Raji cell.
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PMID:Raji cell assay for immune complexes. Evidence for detection of Raji-directed immunoglobulin G antibody in sera from patients with systemic lupus erythematosus. 699 84

We previously reported that rheumatoid factors (RFs) might bear the internal image of Fc gamma-binding proteins (FcBPs) of herpes family viruses, suggesting the possibility that some RFs may be produced as antiidiotypic antibodies to anti-viral FcBP antibodies. Since human cytomegalovirus (HCMV) has been implicated in the pathogenesis of RA, we made an attempt to detect antibodies to 65 KD major HCMV FcBP in sera and synovial fluid from patients with RA. Western blotting was performed using HCMV-infected MRC-5 cell lysate as the antigen. Eleven of 23 patients with RA possessed strong serum antibodies to HCMV-65 KD protein, whereas such antibodies were found in only 2 of 23 normal controls. In the synovial fluid, 10 of 19 RA patients showed anti-HCMV 65 KD reactivity. Pepsin-digested IgG retained anti-65 KD reactivity, indicating that false-positive reaction due to the presence of IgG Fc portion and/or RF was unlikely. 65 KD protein was shown to be different from human heat shock proteins (hsps) using monoclonal antibodies against human hsps. Patients' IgG F(ab')2 also reacted with the 65 KD protein of purified HCMV virion itself. These results support the possibility that some RFs could be produced as antiidiotypic antibodies to anti-viral FcBP antibodies.
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PMID:Antibodies to human cytomegalovirus 65-kilodalton Fc binding protein in rheumatoid arthritis: idiotypic mimicry hypothesis of rheumatoid factor production. 821 29

Human platelets are known to carry Fc receptors (Fc R), but the binding characteristics between ligands and Fc gamma R has not been well elucidated. In this study, we investigated the binding kinetics of IgG Fc fragments (Fc) to Fc R, the association and dissociation characteristics of the ligands to and from Fc gamma R using enzymatically modified Fc fragment derivatives. Approximately 60 minutes and 90 minutes were needed at 37 degrees C and 22 degrees C, respectively, for complete saturation of the Fc binding sites with horseradish peroxidase-conjugated Fc (HPO-Fc). Heat aggregated IgG (HAG) had a greater affinity for the Fc gamma R than Fc monomers. Additional binding of HAG was observed even after the binding sites were saturated with Fc monomers. This could be explained by different binding sites available only for immune complexes or by the partial dissociation of binding sites saturated with Fc by HAG. Further, we noted partial dissociation of HPO-Fc, when HAG was added after saturation of the binding sites with HPO-Fc. In a subsequent experiment, we compared the relative affinities of chemically or enzymatically modified Fc derivatives for Fc gamma R. HAG, which was used as a model for CIC, had a greater affinity for platelet Fc gamma R than IgG monomer and Fc derivatives. Pepsin-digestion of Fc caused a total loss of its affinity for the Fc gamma R, whereas b-mercaptoethanol-treated Fc fragments demonstrated substantial binding to the Fc gamma R. These results indicate that the pepsin digestion affects the Fc portion and causes a disruption in the area of the Fc which is essential for the recognition by the platelet Fc gamma R. On the other hand, cleavage of disulfide bridges by beta-mercaptoethanol resulted in a marked increase in affinity for the Fc gamma R. On the other hand, enzymatic cleavage of the carbohydrate moieties of Fc did not alter the affinity of Fc fragments for the Fc gamma R, indicating that the carbohydrates play an insignificant role or are not involved in their binding to the Fc gamma R.
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PMID:Human platelet Fc receptors: binding kinetics of Fc derivatives to the receptors. 936 89