Dissociation of kappa- and lambda-chains from reduced human immunoglobulins

Differential reduction of interchain disulphide bonds of mouse immunoglobulin G

The relative lability of the interchain disulphide bonds of mouse G(2a)-myeloma protein 5563 was studied as a function of 2-mercaptoethanol concentration. Analysis of partial-reduction mixtures by polyacrylamide-gel electrophoresis and microdensitometry showed that the disulphide bonds between light and heavy chains are much more susceptible to reduction than the bonds between heavy chains. At a low concentration of 2-mercaptoethanol (10mm) the major dissociable products of mouse immunoglobulin G are heavy-chain dimers and free light chains. These findings contrast with the reported behaviour of rabbit immunoglobulin G, for which the lability of inter-heavy-chain bonds was found to exceed that of the bonds linking light and heavy chains (Hong & Nisonoff, 1965); the relative stability of rabbit immunoglobulin G interchain bonds was confirmed in the present study. Examination of human immunoglobulin G and an immunoglobulin G (gamma2) of guinea pig showed that at least in the majority of molecules, as with mouse immunoglobulin G, the disulphide bonds between light and heavy chains are more susceptible to reduction than the inter-heavy-chain bonds.

Guinea pig immunoglobulin light chain isotypes. I. Separation of kappa and lambda chains and the identification of three isotypes of the lambda chain constant homology region

The separation of intact kappa chain and two fragments comprising lambda (lambda) chain from immunoglobulin light chain pools isolated from strain 13 guinea pigs is achieved by cyanogen bromide digestion and gel filtration before and after reductive clevage of disulfide bonds. The smaller lambda chain fragment derives from the original carboxyl-terminus of lambda chain. The partial sequence of component tryptic and thermolytic peptides of this thirty-nine residue fragment allowed its complete sequence to be deduced. Three isotypic forms of this lambda chain constant region fragment, distinguished by four residue positions showing alternative amino acids, are found expressed by guinea pigs. Each of these three isotypes is more homologous to the other two than to lambda chains of any other species. The distribution of amino acid substitutions differentiating these isotypes further supports the view that lambda chain isotypes arose in guinea pigs, and in several other species, independently by gene duplication.

Purification of cold agglutinins from patients with chronic cold haemagglutinin disease. Evidence of their homogeneity from starch gel electrophoresis of isolated light chains

A method is described for the large scale purification of serologically active high-titre cold agglutinins from the sera of patients with chronic cold haemagglutinin disease. Eighteen purified cold agglutinins have been reduced and alkylated and separated into heavy and light chain pools by Sephadex G-100 filtration. The isolated light chains were examined by alkaline urea starch gel electrophoresis and found to be far more homogeneous than normal light chains and comparable in some cases to Bence Jones light chains. However, light chains from different cold agglutinins with the anti-I specificity gave different banding patterns; this might be caused by the fact that they are directed against different parts of the I antigen.

Chemical differences between individual human cold agglutinins

The μ- and κ-chains from four human cold agglutinins having anti-I specificity have been analysed:

The κ-chains have either Asp or Glu, but not both, at the N-terminus. This provides additional support for the view that cold agglutinins are of monoclonal origin.

Both heavy and light chains from cold agglutinins vary as much in amino acid composition as do monoclonal chains of a given type chosen at random. The chemical individuality of cold agglutinin μ-chains is shown also by differences in hexose, fucose and glucosamine content.

The apparent lack of correlation between overall antibody activity and chemical composition of constituent peptide chains indicates the need for close definition of combining specificity in structural studies of cold agglutinins.

Specific dimerization of the light chains of human immunoglobulin

1. The light chains of human immunoglobulin were allowed to dimerize in vitro on removal of the dispersing agents acetic acid or urea. 2. On electrophoresis in polyacrylamide gel at pH8.8 the dimers yielded up to nine regularly spaced bands. This approximates to the number of electrophoretic components known to occur among the monomers. 3. Single electrophoretic components of the dimers were isolated from the gel, dissociated into monomers, and subjected as such to electrophoresis in urea-containing gels. Each gave two adjacent bands. 4. Similarly, after all the light chains as monomers had been subjected to electrophoresis in urea-containing gels, single electrophoretic components were isolated and allowed to dimerize. When examined now as dimers in the absence of urea, each component gave two adjacent bands. 5. These findings are explicable on the following basis. (a) The dimerization of the light chains is specific, at least inasmuch as it occurs between monomers of the same electrophoretic mobilities. (b) With the buffer constant, different light chains undergo different changes in net charge on being transferred from urea-containing to urea-free solution; in this way two different chains of the same initial charge can acquire a charge difference of 1. 6. Experiments with Bence-Jones proteins and other homogeneous light chains gave results substantiating the conclusions (a) and (b).

Recombination of heavy and light chains from human immunoglobulins

The recombination of reduced, alkylated heavy and light chains from three IgG, two IgM and one IgA pathological protein and from normal IgG has been quantitatively studied.

All γ, α and μ chains showed some recombination with all κ and λ chains tested. One of the IgG and two of the IgM proteins showed more than 50 per cent recombination and in these there was evidence of a selective reconstitution of autologous chain pairs; the structural features which determine re-association appear to be independent of the electrophoretic mobility, or antigenic and allotypic specificity of the interacting chains. The chains of normal IgG and of three myeloma proteins showed a low percentage recombination and these autologous chain pairs did not combine preferentially. It appears that immunoglobulin chains show a variable ability to regain their native configuration after isolation.

Two pathological κ chains which were identical in electrophoretic mobility and Inv specificity but not equivalent in re-association behaviour showed well marked differences in tryptic peptide patterns. This indicates that the number of chemically distinct human light chains exceeds the forty variants previously postulated on the basis of antigenic, allotypic and electrophoretic differences.

The N- and c-terminal amino acid sequences of the heavy chain from a pathological human immunoglobulin IgG

The heavy chain of a pathological human immunoglobulin IgG and also the Fd fragment have been isolated. No free alpha-amino group was present on either and the N-terminal sequence of both has been identified as pyrrolid-2-one-5-carbonylvalylthreonine. Splitting at the four methionine residues of the heavy chain with cyanogen bromide gave five fractions. The fraction from the C-terminal end of the chain was isolated in high yield and the amino acid sequence was: His-Glu-Ala-Leu-His-Asp(NH(2))-His-Tyr-Thr-Glu(NH(2))-Lys-Ser-Leu-Ser-Leu-Ser-Pro-Gly These results give strong support to the view that the heavy chain of immunoglobulin is a single peptide chain.