Properties of IgA myeloma proteins isolated rom sera of patients with the hyperviscosity syndrome.

Sera, purified myeloma proteins, and urinary proteins obtained from eight patients with igA multiple myeloma were studied by physical-chemical and immunochemical methods. In six patients whose serum viscosity was increased, the sedimentation constants of the principal component of myeloma proteins ranged from 9.1 to 10.2 S. In two patients with nearly normal serum viscosity, the sedimentation constants of these proteins were 6.2 and 7.2 S. IGA-albumin complexes were detected in most of the sera, but invarying amounts; no complexes of ig with amylase, secretory component, or alpha(1)-antitrypsin were observed. Studies on isolated myeloma proteins revealed that all igA proteisn from sera with increased viscosity represented true polymers, linked by disulfide bonds, rather than noncovalently associated aggregates; J chain was detecable by both alkaline-urea disc electrophoresis and immunoelectrophoresis with a monospecific anti-J chain serum. Increased serum viscosity was not related to the igA subclass, L chain type, or the carbohydrate compositions of individual igA myeloma proteins. The urine of five patients contained free light chains corresponding in type to the light chain of the particular igA myeloma protein. However, free J chain was not detected. The immunoelectrophoretic analysis for the presence of J chain in sera of myeloma patients may be used for early and simple detection of polymeric forms of myeloma proteins.

Identification and properties of J chain isolated from catfish macroglobulin.

After the cleavage of disulfide bonds of macroglobulin isolated from channel catfish (Ictalurus punctatus), an electrophoretically fast-moving polypeptide, which resembled human J chain, was released. On a Sephadex G-200 column equilibrated in 5 M guanidine, the elution position of the J chain overlapped with the descending part of the L chain peak. Further purification was achieved by DEAE ion-exchange chromatography. The isolated polypeptide, which had a molecular weight of 14,800 +/- 500, as determined ultracentrifugally by sedimentation equilibrium in 5 M guanidine, contained 7% carbohydrate with one residue of fucose, two of mannose, one of galactose, two of glucosamine, and one of sialic acid per chain. A comparison of catfish and human J chain amino acid analyses showed the former to have a higher content of serine, glycine, and phenylalanine and a lower content of aspartic acid, isoleucine, and arginine. Tryptic peptide maps of catfish and human J chains revealed very few common peptides. Rabbit and guinea pig antisera to human J chain did not cross-react with catfish J chain. Untreated, resuced and alkylated, S-sulfonated, or cyanogen bromide cleaved macroglobulin from the gar (Lepisosteus osseus) contained no polypeptide analogous to either catfish or human J chain by the criteria employed in this study.

Site of J chain attachment to human polymeric IgA.

A fragment containing J chain was released from human polymeric myeloma IgA protein by cyanogen bromide cleavage. The identity of the fragment was determined by its electrophoretic mobility and antigenic determinants. After purification by gel filtrations and DEAE-Sephadex chromatography, this fraction appeared similar (with respect to its amino acid and carbohydrate compositions and its peptide maps) to the J chain isolated from this IgA protein; the molecular weight was 17,000 +/- 100. Upon reduction and alkylation, with subsequent separation of peptides by gel filtration, three components were obtained: the largest component (molecular weight 13,400) corresponded to the N-terminal segment of J chain and contained a homoserine residue, the second corresponded to the C-terminal part of J chain with 13-18 amino acid residues, and the third corresponded to the C-terminal octapeptide of the alpha chain. The data indicate that J chain is attached to alpha chain(s) through the penultimate cysteine residue of the C-terminal octapeptide.