Effects of D-serine on bacterial D-amino acid transaminase: accumulation of an intermediate and inactivation of the enzyme.
Incubation of pure bacterial D-amino acid transaminase with D-serine or erythro-beta-hydroxy-DL-aspartic acid, which are relatively poor substrates, leads to generation of a new absorbance band at 493 nm that is probably the quinonoid intermediate. The 420-nm absorbance band (due to the pyridoxal phosphate coenzyme) decreases, and the 338-nm absorbance band (due to the pyridoxamine phosphate or some other form of the coenzyme) increases. A negative Cotton effect at 493 nm in the circular dichroism spectra is also generated. Closely related D amino acids do not lead to generation of this new absorption band, which has a half-life of the order of several hours. Treatment of the enzyme with the good substrate D-alanine leads to a small but detectable amount of the same absorbance band. D-Serine but not erythro-beta-hydroxyaspartate leads to inactivation of D-amino acid transaminase, and D-alanine affords partial protection. The results indicate that D-serine is a unique type of inhibitor in which the initial steps of the half-reaction of transamination are so slow that a quinonoid intermediate with a 493-nm absorption band accumulates. A derivative formed from this intermediate inactivates the enzyme.
Martinez del Pozo
A
A
Rockefeller University, New York, New York 10021.
Pospischil
M A
MA
Ueno
H
H
Manning
J M
JM
Tanizawa
K
K
Nishimura
K
K
Soda
K
K
Ringe
D
D
Stoddard
B
B
Petsko
G A
GA
D002942:Circular Dichroism; D007700:Kinetics; D012694:Serine / Q000494:pharmacology*; D000637:Transaminases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D012694:Serine; D000637:Transaminases