Studies with 1,1′-Ethylidenebis(tryptophan), a Contaminant Associated with L-Tryptophan Implicated in the Eosinophilia-Myalgia Syndrome

Abstract

L-Tryptophan binds to a rat liver nuclear envelope protein, and this binding is saturable, stereospecific, and of high affinity. Utilizing an in vitro assay of [ 3H]tryptophan binding to rat hepatic nuclear envelopes, we have previously determined that the L-tryptophan obtained from Showa Denko and which was implicated in cases of the eosinophilia-myalgia syndrome (EMS) inhibited [ 3H]tryptophan binding differently than did control L-tryptophan (not implicated in EMS). Therefore, in this study we investigated whether the addition of 1,1′-ethylidenebis(tryptophan) (EBT), a contaminant or impurity in L-tryptophan implicated in EMS, would have an effect. Our results indicate that EBT alone has little inhibitory binding effect compared with that of control L-tryptophan and that when EBT was added to control L-tryptophan the inhibitory binding effort was similar to that of control L-tryptophan alone. On the other hand, in vitro addition of EBT plus L-tryptophan to nuclei of cultured murine macrophages (WLG5) results in less inhibition of [H-3]-tryptophan binding than does addition of L-tryptophan alone. Similar in vitro additions to nuclei of rat brain reveal little effect on binding, as was also the case for hepatic nuclear envelopes. Adding EBT to an in vitro hepatic protein synthesis system and measuring [ 3H]tryptophan incorporation into acid-precipitable proteins reveal that it competes similarly to that found with equimolar concentrations of unlabeled L-tryptophan. It does not affect [ 14C]leucine incorporation into proteins. [ 14C]EBT becomes incorporated in vitro into proteins (acid-precipitable), and this incorporation is diminished in the presence of equimolar concentrations of unlabeled EBT or L-tryptophan. This suggests that EBT or possibly a breakdown product becomes incorporated into proteins. Speculation as to how EBT may affect tissues in experimental animals is presented.