Aluminum inhibition of hexokinase activity in vitro: a study in biological availability.

We have used the HK/G6PDH coupled enzyme assay to determine the biological availability of aluminum in mixed-ligand media of biological interest. The biological availability of aluminum was measured as the inhibition of the activity rate of the assay and was shown to be dependent upon the equilibration state of the aluminum stock solutions (prior to their addition to the assay) and the comparative reaction kinetics of competitive aluminum equilibria in the assays. Aluminum was found to inhibit the assay, however, the inhibition by aluminum was abolished when silicic acid was present in both the aluminum stock solution and the assay medium. The assay is proposed as a model system for investigating the biological availability of aluminum in heterogenous media of biochemical significance.