Characterization of amyloid deposits and P component from a patient with factor X deficiency reveals proteins derived from a lambda VI light chain.

Amyloid fibrils were isolated from a spleen obtained at surgery from a 58-year-old white man with primary amyloidosis presenting with factor X deficiency and responding dramatically to splenectomy. Gel filtration on Ultragel ACA 54 in 5 M guanidine 1 M acetic acid yielded components with molecular weights between 17,000 and 13,000. Two of them (17K and 15K) were studied in detail. Antigenic and amino acid sequence analysis showed that these proteins were related to lambda VI immunoglobulin light chain. The predominant protein subunits of the amyloid fibril of the deposits (17K) was processed at the carboxy terminus in the same section of the constant region as the only other lambda VI amyloid protein previously reported. Amino terminal sequence of the 15K protein revealed not only degradation at the C terminal, but also minor degradation at the amino terminal (three residues difference from the 17K species). P component was also isolated from the spleen and characterized. This represents the first antigenic and sequence analysis of tissue amyloid proteins and P component from a patient presenting with factor X deficiency and another example of amyloid proteins derived from the newly discovered amyloidogenic lambda VI light chain subgroup.