Binding of Aldolase and Triosephosphate Dehydrogenase to F‐Actin and Modification of Catalytic Properties of Aldolase

The binding of aldolase and triosephosphate dehydrogenase to F‐actin was studied in vitro under various conditions. Several monovalent and bivalent cations and anions, most of the glycolytic metabolites, and some nucleotides were examined with respect to their influence on the binding. Desorption of the bound enzymes as well as adsorption hindrance may be due to relatively specific factors (metabolites, ions) and relatively non‐specific factors (pH, ionic strength). In the case of aldolase it was found that fructose‐1,6‐diphosphate, dihydroxyacetone phosphate, ATP, ADP, and inorganic phosphate cause a marked adsorption hindrance within their physiological concentration ranges. In analogy with the effect of fructose‐1,6‐diphosphate on aldolase, the binding of triosephosphate dehydrogenase to F‐actin is also inhibited most strongly by its substrate glyceraldehydephosphate. However, adsorption hindrance of triosephosphate dehydrogenase is also caused by fructose‐1,6‐diphosphate, ATP, and inorganic phosphate, although higher concentrations of these compounds are needed in comparison with aldolase. Kinetic studies of F‐actin‐bound aldolase revealed that the properties of the enzyme are modified by the binding. Under the chosen experimental conditions, binding of aldolase to F‐actin doubles V max and increases K m for fructose‐1,6‐diphosphate by almost one order of magnitude. K m determinations were performed in the absence of ammonium sulfate. Sulfate and also phosphate anions are strong inhibitors of muscle aldolase. In both cases the inhibition type appears to be competitive. Determinations of K m for fructose‐1,6‐diphosphate of native muscle aldolase gave values as low as 0.4 μM.