Sb. Lee et Jf. Robyt, Trapping of a covalent enzyme intermediate in the reaction of Bacillus macerans cyclomaltodextrin glucanyltransferase with cyclomaltohexaose, CARBOHY RES, 336(1), 2001, pp. 47-53
The mechanism of catalysis of Bacillus macerans cyclomaltodextrin glucanylt
ransferase (CGTase, EC 2.4.1.19) was studied by trapping and isolating a co
valent-enzyme intermediate. CGTase catalyzes an acceptor or coupling reacti
on between cyclomaltohexaose and a carbohydrate acceptor such as D-glucose.
CGTase was incubated with H-3-labeled cyclomaltohexaose in the absence of
any added acceptor. After 30 s of reaction, the enzyme was rapidly denature
d and precipitated by the addition of 10% trifluoroacetic acid (TFA). Exten
sive washing of the precipitated protein showed retention of radioactivity
with the protein. The precipitate was dissolved in 0.1 M TFA, containing 6
M urea and passed over a BioGel P-10 column. The protein fraction retained
95% of its original radioactivity. The reaction with [H-3]cyclomaltohexaose
was also stopped by the addition of TFA to give an inactive enzyme at pH 2
.5. The enzyme was separated from unreacted cyclomaltohexaose on a BioGel P
-10 column and was shown to be radioactive. When the radioactive protein fr
action was rechromatographed on BioGel P-10, it retained 100% of the label.
These results demonstrate the formation of a covalent carbohydrate-enzyme
intermediate in the reactions catalyzed by CGTase. (C) 2001 Elsevier Scienc
e Ltd. All rights reserved.