Catalytically important amino acid residues in endoglucanases from a mutant strain Trichoderma sp. M7

Two endoglucanases, EG-III (49.7 kD) and EG-IV (47.5 kD), from a mutant strain Trichoderma sp. M7 were modified with several specific reagents. Water-soluble carbodiimide completely inactivated only one of the purified endoglucanases and kinetic analysis indicated that at least two molecules of carb...

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Bibliographic Details
Published in:Biochemistry (Moscow) 2006, Vol.71 Suppl 1 (S1), p.S25-S30
Main Authors: Petrova, S D, Bakalova, N G, Kolev, D N
Format: Article
Language:English
Subjects:
Amino acids
Bacterial Proteins - chemistry
Bromosuccinimide - chemistry
Catalysis
Catalysts
Cellulase - antagonists & inhibitors
Cellulase - chemistry
Inactivation
Mutation
Reagents
Trichoderma - enzymology
Tryptophan - chemistry
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Summary:Two endoglucanases, EG-III (49.7 kD) and EG-IV (47.5 kD), from a mutant strain Trichoderma sp. M7 were modified with several specific reagents. Water-soluble carbodiimide completely inactivated only one of the purified endoglucanases and kinetic analysis indicated that at least two molecules of carbodiimide bind to EG-IV for inactivation. The reaction followed pseudo-first-order kinetics with a second-order rate constant of 3.57 x 10(-5) mM(-1) x in(-1). Both endoglucanases were inhibited by iodoacetamide, but the absence of substrate protection excluded direct involvement of cysteine residues in the catalysis. N-Bromosuccinimide (NBS) showed a strong inhibitory effect on both endoglucanases, suggesting that tryptophan residues are essential for the activity and binding to the substrate, since the presence of substrates or analogs prior to NBS modification protected the enzymes against inactivation.
ISSN:0006-2979
1608-3040
DOI:10.1134/S0006297906130049