Cyclomaltodextrin glucanotransferase from Bacillus circulans E 192: nitration with tetranitromethane.
Nitration of tyrosine residues was performed on Bacillus circulans E 192 cyclomaltodextrin glucanotransferase (CGTase) using tetranitromethane (TNM). A maximum of 15 out of 28 tyrosine residues is modified with 8 mM TNM, entailing a concomitant loss of enzymic activity and tryptophan fluorescence. Spectroscopic studies suggest that these two phenomena are related to an impairment of the enzyme conformation as a consequence of the tyrosine nitration. The presence of 5 mM acarbose during the CGTase nitration results in the protection of one tyrosine residue and the rate of inactivation is reduced 9.4-fold. These results support a contribution of a tyrosine residue in the CGTase catalytic site. The nitration of CGTase also entails a decrease in the enzyme's affinity for a beta-cyclodextrin (beta-CD) co-polymer. Kinetic and analytical investigations on isolated modified enzymes support the concept that this phenomenon is unrelated to the modification of tyrosine residues, but rather concerns a side reaction of the reagent occurring at the raw-starch-binding site of the CGTase.
Villette
J R
JR
Laboratoire de Chimie Biologique, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France.
Helbecque
N
N
Albani
J R
JR
Sicard
P J
PJ
Bouquelet
S J
SJ
D020909:Acarbose; D001407:Bacillus / Q000201:enzymology*; D002942:Circular Dichroism; D005964:Glucosyltransferases / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D009566:Nitrates / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013774:Tetranitromethane / Q000378:metabolism*; D014312:Trisaccharides / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
D009566:Nitrates; D014312:Trisaccharides; D014443:Tyrosine; D005964:Glucosyltransferases; C019963:cyclomaltodextrin glucanotransferase; D013774:Tetranitromethane; D020909:Acarbose