PROPERTIES OF CRYSTALLINE l-ASPARTATE 4-CARBOXY-LYASE FROM ACHROMOBACTER SP.

Abstract

L-Aspartate 4-carboxylyase formed regular hexagonal plates on crystallization. The decarboxylation of L-aspartate (Km80uM) at pH 5.0 was competitively inhibited by DL-erythro-/3-hydroxyaspartate (Ki 320 uM) and DL-threo-B-hydroxy-aspartate (Ki 11 uM). The enzyme was maximally active over a wide range of pH (3.5-6.0). It exhibited a spectral peak at 360 mu in this pH range. Cyanide or hydroxylamine and other carbonyl reagents inhibited the enzyme. The activation of freshly prepared enzyme by 2-oxo acids and by glyoxal was observed only at high concentrations of L-aspartate. Reduction with sodium-borohydride inactivated it and produced a pyridoxyl derivative covalently bound to a group on the protein. L-Aspartate and erythro-B-hydroxyaspartate reacted with the enzyme to give derivatives with maximum extinction at 325 mu. The erythro-B-hydroxyaspartate derivative was not reduced by sodium-borohydride. Activity was partially recovered after dialysis. The role of derivatives in the mechanism of L-aspartate decarboxylation is discussed.