l -Serine Deaminase of Escherichia coli

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Abstract
The native l -serine deaminase ( l -serine hydrolyase, deaminating, EC 4.2.1.13) of Escherichia coli K-12, which seems to be a very labile protein, is rather stable in concentrated solution. Dilution rapidly inactivates it, but in the presence of a saturating concentration of l -serine the molecule is protected from inactivation. It is a very specific enzyme; l -serine is the sole substrate with a K m value of 6.60 × 10 −3 m. d -Serine and l -cysteine are competitive inhibitors. Substrate saturation curves of the native enzyme show sigmoid shape, whereas the enzyme liberated from the bacteria in the presence of l -serine exhibits normal Michaelis-Menten kinetics.