Permeability studies on horse liver alcohol dehydrogenase (HLAD) in polyacrylamide gel beads

Polyacrylamide gel beads with monomer concentrations ranging from 5 to 30% and with constant degree of cross-linking (5%) were prepared. Dried beads were swollen in buffered HLAD/NAD+ solutions and placed in a water-immiscible organic solution of substrates. Increased enzymatic activity was observed in beads with higher polymer density. Evidence is given that catalyst in the high-density polymer is concentrated in the outer part of the beads, but is homogeneously distributed in low-density polymers. This was clearly visualised by high-resolution NMR imaging on gel beads impregnated with Gd-DTPA-labeled HLAD. Furthermore, reaction rates were higher for larger beads.