A human myeloma immunoglobulin G binding four moles of calcium associated with asymptomatic hypercalcemia

Giampaolo Merlini, Lorraine A. Fitzpatrick, Ethel S. Siris, John P. Bilezikian, Steven Birken, Sherman Beychok, Elliott F. Osserman

Research output: Contribution to journalArticle

Abstract

A calcium-binding immunoglobulin G (IgGIλRUP) was identified in the serum of a patient with multiple myeloma, asymptomatic hypercalcemia, and a normal ionized serum calcium. Calcium binding by IgGRUP was confirmed by two-dimensional electrophoresis with calcium-45 and equilibrium dialysis. Amino acid analyses indicated an unusually high number of glutamic (or glutamine) residues in the L chain and Fab fragment but no detectable γ-carboxyglutamic acid. As determined by equilibrium dialysis with45Ca, the intact IgGRUP and its Fab fragments bound calcium at an optimum pH of 7.4. There was minimal binding of calcium to H chains and no binding by L chains or the Fc fragment. Recombination of H and L chains partially restored the binding activity. By Scatchard analysis, the binding affinity (Kd) of IgGRUP was 1.7×10-3M and the binding capacity was 4 mol of calcium/mol of IgG. The binding of 4 mol of calcium/mol of IgG is twice that reported previously for two other calcium-binding myeloma proteins and suggests unique properties of IgGRUP.

Original languageEnglish
Pages (from-to)185-196
Number of pages12
JournalJournal of Clinical Immunology
Volume4
Issue number3
DOIs
Publication statusPublished - May 1984

Keywords

  • calcium binding
  • IgG
  • Myeloma

ASJC Scopus subject areas

  • Immunology and Allergy
  • Immunology

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