A study was made of the stability of crude hog kidney D-amino acid oxi
dase (D-AAO) under different experimental conditions of temperature, e
nzyme concentration, buffer and in the presence of flavine adenine din
ucleotide (FAD) and glycerol. A deactivation mechanism is proposed. Th
e kinetic deactivation studies were performed in a buffer at pH 8 over
a temperature range of 277-327 K (4-54 degrees C). The activity for D
-AAO at 1 U/ml at 277 K in potassium phosphate and potassium pyrophosp
hate buffer remains almost constant for 20 days. For D-AAO at 0.02 U/m
l at 303 K (30 degrees C) in phosphate buffer, the presence of FAD and
glycerol causes the deactivation constant to decrease, while the init
ial activity and the half-life time increase, the latter doubting on p
assing from buffer alone to buffer with FAD and 10% glycerol. In the c
ase of D-AAO at 0.2 U/ml, the stability increases considerably with re
spect to 0.02 U/ml. Both FAD and glycerol enhance this stabilization.
For temperatures above 313 K (40 degrees C), the deactivation of D-AAO
at 0.2 U/ml showed values of the thermodynamic variables for the over
all deactivation constant and for the deactivation constant due to the
loss of FAD that indicate that the dissociation of FAD is the main de
activation mechanism. Finally, deactivation due to the loss of FAD is
higher for D-AAO at 0.1 U/ml as compared with a concentration of 0.2 U
/ml.