Bence-Jones proteins and light chains of immunoglobulins. 10. Luminescence studies on Bence-Jones proteins and light chains of immunoglobulins and their subunits

To provide information on the tertiary structure of the antibody molecule we have investigated the luminescent properties of the light polypeptide chain of human immunoglobulins. The fluorescence and phosphorescence yields, spectra, lifetimes, and anisotropies of a large number of homogeneous light chains, i.e., Bence--Jones proteins and light chains derived from myeloma proteins, were measured. No two proteins gave identical tyrosyl or tryptophyl fluorescence spectra in comparative studies on over 75 proteins belonging to the four basic subgroups of kappa chains and of lambda chains. Spectral differences were apparent even among proteins exhibiting more than 85 percent amino acid sequence identity. The fluorescence yields of tyrosine and tryptophan varied 10- and 100-fold, respectively; the Stokes' shift of tryptophan ranged from 328 to 365 nm, but that for tyrosine was apparently invariant (305 to 307 nm). Emission as well as excitation spectra showed tyrosyl and tryptophyl residues interact minimally or not at all. Fluorescence lifetimes of the tyrosyl and tryptophyl contributions were measured separately, and the apparent natural lifetimes were calculated. Proteins could be grouped in accordance with similarities in fluorescence lifetimes and fluorescence yields; there was no evident relationship between these groupings and the light chain type (kappa or lambda), aminomore » acid sequence, or tryptophan content.« less