Kinetics of soluble and collagen-bound aspartate aminotransferase: diffusional effects with a two-substrate enzymatic reaction.

The kinetic properties of aspartate aminotransferase covalently bound to collagen are compared to those of the free enzyme. In the bound state, the enzyme exhibits a greater affinity for glutamate, but a lower affinity for oxalacetate. In order to assess precisely the contribution of diffusional limitations on the heterogeneous enzyme kinetics, a simple modeling of diffusional effects on a two-substrate enzymatic reaction is developed. According to this quantitative analysis, diffusional limitations for oxalacetate alone account for the increased and decreased enzyme affinities toward its two substrates. Consequently, coupling of the enzyme to collagen does not significantly affect its intrinsic kinetic properties.