Characterization of an L-serine dehydratase activity in permeabilized cells of Brevibacterium linens ATCC 9175

Brevibacterium linens ATCC 9175 praduces large quantities of, ammonia and pyruvate (rom L-serine. This reaction occurs via an L-serine dehydratase (EC.4.2.I.13), whose activity is maximal at the end of exponential growth on rich medium and which abruptly decreases at the beginning of the stationary phase. ft is not possible ta extract the soluble form of the enzyme without a total loss of activity. Subcellular localization studies after creating stable proto- plasts with lysozyme have shawn that a part of the activity is bound ta cell membranes. A stable (orm of activity has been obtained by treating the cells with Triton X-IOO and the main properties of the enzyme have been studied with this insoluble form. The apparent Michaelis constant is 50 mM and the Vmax is 200 nmol of pyruvate formed per minute and per mg of dry extract. The optimum pH is included between 8.5 and 9.4 anâ activity is very stable between 8.0 and 9.4. The enzyme is slightly thermostable. The exclusive substrate is L-serine. D-serine and 2-aminoethanol are competitive inhibitors. L-serine dehydratase activity is strongly inhibited by o-phenanthraline. Pyridoxal phosphate is required for maximum activity.