| Abstract: | Amyloid fibril proteins were isolated from the spleen of a patient with IgD(lambda)-plasmocytoma by extraction and gel filtration in 5M guanidine hydrochloride. The molecular mass of the predominant polypeptide chain was approximately 5000 Da. Its complete amino-acid sequence was elucidated by stepwise automated degradation of the carboxymethylated polypeptide chain and by structural studies of tryptic and thermolysinolytic cleavage products. The length of the polypeptide chain was 58 to 59 residues and it was homologous to the amino acids in positions 8 through 65 of the variable part of an lambda-type immunoglobulin light chain, which was most closely related to the lambda II subgroup. The N-terminal sequence of this amyloid fibril protein proved to be heterogeneous, indicating cleavage after the amino acids in positions 7 and 8. Peptides from the constant part of the lambda-chain were unexpectedly found in the tryptic digest of the denatured amyloid protein HAR. One polypeptide derived from the constant region was separated from the main component by high performance liquid chromatography. Its amino-acid sequence commenced at position 111 and could be traced in 41 steps. In this case, at least two constant region fragments were shown to be constituents of the amyloid fibril protein. The association of fragments from the variable as well as the constant region is discussed with respect to amyloid formation. |
