Histamine as a ligand in blood plasma. Part 6. Aspartate and glutamate as possible partner ligands for zinc and histamine to favour histamine catabolism.

The hypothesis was recently put forward that the diffusion of plasma histamine into the environmental tissues in which the mediator is catabolized, may occur passively in the form of the zinc-histamine-cysteinate complex. In accordance with this hypothesis, any partner ligand for zinc and histamine in which raising plasma concentration would entail a better mobilization of histamine into neutral diffusable metal complexes would also favour the histamine catabolism. Such a role was envisaged in the present work for aspartate and glutamate. Their efficiency in that respect was tested on the basis of computer simulations using the equilibrium constants of the corresponding zinc-histamine-aspartate and zinc-histamine-glutamate complexes, which were determined beforehand under the plasma conditions of temperature, ionic strength and isotonicity. It was established that aspartate and glutamate plasma concentrations should be raised 1000 and 400 times over their respective normal levels before the combination of each of these amino-acids with zinc within the same increase ratio becomes more efficient than zinc ions alone.