title: Kinetics of the allosteric transition of aspartate transcarbamylase. Chemical quench studies.
abstract: Using a chemical quench device, the rate of synthesis of carbamyl aspartate from the substrates aspartate and carbamyl phosphate was followed as a function of the time between mixing the enzyme with substrates and quenching with trichloroacetic acid. This function, which is linear at long times, shows (at 4 degrees C) a transient lag phase of product of roughly 10 ms. However, when the catalytic subunit (in which the enzymatic activity is desensitized) is used instead of the enzyme, the lag disappears. Therefore the lag seems to be associated with the control functions of the enzyme, i.e. to represent the allosteric transition involved in substrate-substrate (homotropic) co-operativity. Thus the relaxation time for the activation process is roughly 10 ms. The implications of these results are examined.
mesh_terms: D000494:Allosteric Regulation; D001221:Aspartate Carbamoyltransferase / Q000378:metabolism*; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000096:biosynthesis; D001665:Binding Sites; D004926:Escherichia coli / Q000201:enzymology; D007700:Kinetics; D013997:Time Factors
chemical_list: D001224:Aspartic Acid; D001221:Aspartate Carbamoyltransferase; C006893:ureidosuccinic acid