NMR-STUDIES OF COPPER SPECIATION IN THE BOVINE RUMEN ENVIRONMENT

Dietary copper supplements containing complexed copper have been asser ted to be more bioavailable than 'inorganic' supplements. Since bioava ilability is intimately related to the particular metal ion species th at exist in any given environment, studies of solution speciation can be used to examine this assertion. In a previous study, our computer m odeling of copper speciation in bovine saliva indicated that when a ly sine-complexed copper supplement is used, the complex will not persist . In the present study, these conclusions are supplemented and extende d using H-1 NMR experiments. Lysine and the copper(II)-lysine system a re characterized, and chemical shifts of the individual species obtain ed. Chemical shift values for the copper(II)-lysine-bovine saliva syst em can then be predicted. Results show good agreement with experimenta l values. The scope of the computer modeling is then expanded to inclu de the major low molar mass ligands present in the rumen. Implications of the results are discussed. The validity of this rumen model is fur ther evaluated by NMR investigations on biological samples. The study provides further evidence that complexes such as copper(II)-lysine wou ld disintegrate in the gastrointestinal tract, and are unlikely to be absorbed intact. (C) 1998 Elsevier Science Inc. All rights reserved.