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Biomedical subjects

R M Chapuis

Publications and source records attributed to R M Chapuis.

12 recordsLinked to original sources
PubMed1982

Structural and functional studies in C1q deficiency.

The sera of two brothers were found totally lacking hemolytic C activity. One of them, a 16-yr-old male, presented a severe lupus-like syndrome, whereas the other was apparently healthy. Immunochemical quantitation of C components in both sera showed depressed levels of C1q, whereas the levels of C1r, C1s, and C1 inhibitor were elevated. C4, C3, C5, factor B, and beta 1H levels were in the normal range. Hemolytic C1 activity was totally lacking. C4 titers were elevated (150% of normal). C2 hemolytic activity was about one-third of normal, and the titers of the terminal components C3-C9 were also reduced in the two siblings. Double immunodiffusion against anti-C1q antiserum showed a partial loss of C1q antigenic determinants in the two siblings. Furthermore, the C1q of both siblings was unable to interact with immunoglobulins or to associate with C1r and C1s. Addition of purified human C1q to the sera restored their total C and C1 hemolytic activity. The dose response to the C1q addition was linear, indicating that the functional deficiency was not due to the presence of a serum inhibitor. Although antigenically deficient in comparison with normal C1q, the abnormal C1q appeared to have a larger m.w., as determined by gel chromatography. Investigation of other members of this family suggests a genetically linked disorder, because four out of six siblings had the same dysfunctional C1q in their serum.

Adolescent↗
PubMed1980

The first component of complement. I. Purification and properties of native C1.

The first component of complement has been purified by using affinity chromatography on Sepharose-bound IgG. Unlike earlier procedures that yield the activated form of C1, in this method C1 is maintained in the native form by the protease inhibitor p-nitrophenyl, p'-guanidinobenzoate (NPGB). The procedure requires only two steps and yields pure C1 as judged both by SDS-PAGE analysis and by effective molecule calculations. The yields have varied from 30 to 50% in over 50 preparations. The functional properties of the purified native C1 correspond to those of C1 in serum. The dose-response activity profile is nonlinear, but becomes linear when C1 IS ALLOWED TO SELF-ACTIVATE. From SDS-PAGE analysis of the self-activated C1, all the C1r and C1s subcomponents are converted to the activated split products, indicating that all C1 molecules are biologically active. The recovery of C1 activity is dependent on the use of a heterologous source for the IgG on the affinity absorbant. The conditions of binding and elution from the Sepharose-IgG column are critical, indicating that immunoglobulin-bound C1 is rapidly inactivated under physiologic conditions by serum inactivators. The activation of the purified C1 in fluid phase has been explored both in the presence and absence of C1-inhibitor.

Benzoates↗
PubMed1977

Selective proteolysis of the J chain component in human polymeric immunoglobulin.

To clarify the losses that have been observed in the J chain portion of human IgM and IgA, were carried out studies on the enzymatic susceptibility of the J polypeptide. When Waldenström macroglobulins and myeloma IgA polymers were subjected to limited proteolysis with various endopeptidases, only subtilisin was found to attack the J chain component. The pattern of cleavage was a function of the polymer species. The J chain in IgM was highly susceptible to digestion, quantitative cleavage being achieved at very low enzyme to IgM ratios and without significant changes in the remaining pentamer structure. Analyses of the digestion products showed that the initial cleavage occurred at an exposed region midway in the J sequence and was followed by extensive degradation of the carboxy-terminal segment. These findings indicated that the observed loss of the IgM J component can be explained by the inadvertent introduction of subtilisin in vitro or by the attack of in vivo enzymes with a specificity similar to subtilisin. In contrast, the IgA J chain was found to be much more resistant to subtilisin proteolysis; its cleavage required higher enzyme concentrations and was accompanied by significant degradation of the alpha-chains. Thus, it appears unlikely that the IgA J polypeptide is degraded by either in vitro or in vivo enzymes unless its accessibility is first enhanced by changes in the IgA Fc structure.

Amino Acid Sequence↗
PubMed1975

Linkage and assembly of polymeric IgA immunoglobulins.

The intersubunit linkage of polymeric IgA immunoglobulins was determined from studies of the products of reductive and cyanogen bromide cleavage. Under conditions of limited dithioerythritol reduction tetramer IgA molecules were cleaved to yield two monomers and a J chain containing dimer. The stability of the dimer and the conservation of the J chain disulfides indicated that the J chain joins two monomer subunits. Evidence confirming the J chain dimer clasp was obtained from the depolymerization of tetramer and dimer IgA by cyanogen bromide treatment. The cleavage studies also showed that (a) the S-S bonds directly joining the other subunits are located at the same penultimate alpha chain half-cystines that constitute the site of J chain attachment and (b) during limited reduction the monomer-monomer bonds undergo interchange to release subunits without a concomitant generation of alpha chain thiols. These linkage data provide strong support for the assembly of IgA and IgM polymers by sequential disulfide exchanges beginning with the formation of a J chain containing dimer.

Chemical Phenomena↗
PubMed1974

Mechanism of IgM polymerization.

The stoichiometry of J chain in pentamer IgM has been determined by measuring the radiolabeled thiols in the constituent chains after complete reduction and alkylation of the polymer. One mole of J was found to be disulfide bonded to 1 mol of pentamer. The linkage of J chain in IgM has been determined by correlating the J disulfides cleaved with the subunits released after limited reduction and alkylation of the polymer. The analyses showed that: (a) Significant amounts of monomers, as well as small quantities of dimers, trimers, and tetramers, were generated by the reducing conditions employed. (b) The number of J disulfide bonds broken did not correspond to the extent of depolymerization. (c) No J disulfides were cleaved in the J-containing dimer products of the limited reduction. These data demonstrated that the J chain is located as a disulfide clasp between two of the IgM monomer subunits. From the observed linkage, the assembly of IgM is postulated to proceed by a series of sequential disulfide exchanges beginning with the formation of the J-containing dimer.

Alkylation↗