Chemical Modification of ε-Amino Groups in Glutamine Synthetase from Bacillus stearothermophilus with Ethyl Acetimidate

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Abstract
The activity of glutamine synthetase [EC 6·3·2·1] from Bacillus stearothermophilus decreased slightly on modification with ethyl acetimidate. Acetamidination of 25–26 of the 27 ε-amino groups/subunit of the enzyme affected the maximum velocity, but not the Michaelis constant. The thermostability of the enzyme was considerably increased on acetamidination. Acetamidination of the enzyme did not affect the circular dichroism, the tryptophan fluorescence or the quenching effects of KI and acrylamide on the tryptophan emission. The fluorescence spectrum of p-toluidinylnaphthalene sulfonate bound to the enzyme changed on acetamidination.