6.3.4.2 - 6.3.4.2 by using talon metal affinity resin, a glass Econo-Column and a Sephadex G-50 column. Proteolysis is performed at 23°C for 40 min. The protein solution is then loaded again on a Talon resin column but this time the flow-through, containing CTPS without His tag, is collected. Finally the protein is loaded onto a 0.2-ml SourceQ15 medium column. 6.3.4.2 enzyme is purified by gel filtration on a HiLoad 26/60 Superdex 200 column. Active fractions are pooled and applied to a Mono Q HR 5/5 column. Final purifications step is performed on a HiLoad 26/60 Superdex 75 column. The isolated EcCTPS is found >90% pure as judged by SDS-PAGE and ESI-MS. 6.3.4.2 His6-tagged human CTP synthetase 1 is purified by loading onto a Ni2+-NTA column 6.3.4.2 His6-tagged wild type and mutant human CTP synthetase 1 enzymes are expressed and purified from yeast cell extracts with Ni2+-NTA resin 6.3.4.2 His6-tagged wild type human CTP synthetase 1 is expressed and purified from Escherichia coli by Ni2+-NTA chromatography and with PorosHQ-ion-exchange chromatography 6.3.4.2 Ni2+-IDA resin column chromatography 6.3.4.2 partial 6.3.4.2 protein is purified by using HisTrap HP and Superdex 75 columns 6.3.4.2 recombinant wild-type and mutant enzyme L109A