Search PubMedSearch

PubMed · 7008970

Normal range for the third component of complement by solid-phase immunofluorescence.

Abstract

The source did not provide an abstract. Follow the original record for more information.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

M K Fleetwood, B A Maier, S H Lewis. 1981. Normal range for the third component of complement by solid-phase immunofluorescence.. https://pubmed.ncbi.nlm.nih.gov/7008970/

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

The internal thioester and the covalent binding properties of the complement proteins C3 and C4.

The covalent binding of complement components C3 and C4 is critical for their activities. This reaction is made possible by the presence of an internal thioester in the native protein. Upon activation, which involves a conformational change initiated by the cleavage of a single peptide bond, the thioester becomes available to react with molecules with nucleophilic groups. This description is probably sufficient to account for the binding of the C4A isotype of human C4 to amino nucleophiles. The binding of the C4B isotype, and most likely C3, to hydroxyl nucleophiles, however, involves a histidine residue, which attacks the thioester to form an intramolecular acyl-imidazole bond. The released thiolate anion then acts as a base to catalyze the binding of hydroxyl nucleophiles, including water, to the acyl function. This mechanism allows the complement proteins to bind to the hydroxyl groups of carbohydrates found on all biological surfaces, including the components of bacterial cell walls. In addition, the fast hydrolysis of the thioester provides a means to contain this very damaging reaction to the immediate proximity of the site of activation.

Complement C3

Investigation of mechanism-based inhibitors of complement targeting the activated thioester of human C3.

An intramolecular thioester bond in complement protein C3 is vital for covalent attachment of C3b (the proteolytically activated form of C3) to biological surfaces and for activation of the complement system. Proteolytic removal of C3a from C3 activates the thioester in the C3b fragment. Activated C3b primarily forms ester bonds with hydroxyl groups of carbohydrates on complement activating surfaces, but it has also been shown to react with the hydroxyl group of tyrosine and with specific Ser and Thr residues on IgG and on complement protein C4b. To examine the reactivity of the thioester, several families of hydroxylated compounds were examined. Reactivity of a series of substituted phenols varied over two orders of magnitude and demonstrated a linear correlation between reactivity and the Hammett substituent constants. Hydroxylated drugs including members of the L-DOPA/epinephrine family and hydroxamic acids also were examined. Compounds were identified that were 20,000 times more reactive than carbohydrates. These compounds were found to inhibit both the classical and alternative pathways of complement activation. Although the specificity of the thioester for its natural biological targets appears to be determined by many structural features, the data presented here demonstrate that increasing the nucleophilic character of the target hydroxyl group can increase the potency of a synthetic inhibitor many orders of magnitude.

Complement C3

Polymer agglutination-based piezoelectric immunoassay for the determination of complement III.

A piezoelectric immunoassay technique, which is based on the detection of agglutination of antibody- or antigen-bearing polymer by an immunoreaction using a piezoelectric quartz crystal, has been developed for the determination of complement III (C3). Anti-C3 antibodies were physically adsorbed onto the carboxymethyl cellulose polymer by hydrogen bonds. The agglutination of the (anti-C3 antibody)-bearing polymer by immunoreaction caused a viscosity change of the solution, which could be monitored by a piezoelectric quartz crystal. The effect of experimental conditions such as the polymer concentration, the antibody dilution ratio and the reaction temperature on the frequency response were investigated. The linear ranges for C3 concentration determined by the end-point method and the initial rate method were 22.0-43.2 micrograms ml-1 and 22.0-49.1 micrograms ml-1, respectively. Other antigens presenting in serum did not interfere with the determination of C3. Analytical results of ten clinical specimens obtained using the developed technique were in satisfactory agreement with those given by the rate diffusion turbidimetry. With a simple regeneration method devised, the crystal can be used repeatedly with acceptable reproducibility.

Complement C3