A study of the interactions of an immunoglobulin light chain with artificial and B-lymphocyte membranes.

The binding of an immunoglobulin lambda light chain (IgLC) to synthetic and biological membranes was monitored in real-time using a recently developed, time-resolved fluorescence technique. Lambda IgLC purified from the urine of patients with multiple myeloma, were used in studies of protein-membrane interactions. The association of the lambda IgLC dimer with B-lymphocytes was shown to be stabilised predominantly by non-polar interactions. Furthermore, it was found that following binding to synthetic phospholipid membranes, a reorientation of the light chain occurred which resulted in a change in the distribution of charged residues at the lipid-water interface. The rate constants associated with the binding event were calculated, and appear to comprise both temperature insensitive and sensitive components. The calculated activation energies of the binding and reorientation events were found to be 13.53 KJmol(-1) and 87.89 KJmol(-1), respectively. The large activation energy associated with the reorientation phase suggests the movement of large protein domains, possibly involving a whole immunoglobulin domain. The binding and reorganisation of the IgLC upon the phospholipid membrane may confer novel biological functions to the bound protein and potentially contribute to such phenomenon as myeloma-associated immuno-suppression.

Inhibition of proliferation of human leukaemia 60 cells by methylglyoxal in vitro.

Methylglyoxal (2-oxopropanal) is the physiological substrate of the glyoxalase system. When exogenous methylglyoxal (50 microM-1 mM) was added to human leukaemia 60 (HL60) cells in culture (5 x 10(4) cells/ml), inhibition of growth and toxicity was induced. The median growth inhibitory concentration IC50 value was 238 +/- 2 microM. There was little differentiation of HL60 cells induced by methylglyoxal (a maximum of 2% differentiation with 500 microM methylglyoxal). There was no similar toxicity induced by methylglyoxal in corresponding differentiated cells, neutrophils, under the same culture conditions. Cell growth and toxicity induced by methylglyoxal (250 microM) in HL60 cells occurred in the initial 24 h of culture, after which residual surviving cells exhibited normal growth kinetics. It could also be prevented by replacing the culture medium in the initial 6 h of culture; thereafter, irreversible toxicity developed, reaching the maximum value after 24 h of culture. Growth arrest and toxicity induced by methylglyoxal increased with increasing serum composition of the medium. The mechanism of toxicity is unknown.