2Barcelona University, Barcelona 08028, Spain
3Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, 119991 Moscow, Russia; fax: (495) 939-4195
4Institute of Biochemistry, National Academy of Sciences of Belarus, Bulvar Leninskogo Komsomola 50, 230017 Grodno, Belarus; fax: (0152) 43-4161
* To whom correspondence should be addressed.
Received July 17, 2008; Revision received October 6, 2008
Catalytic activity of two active sites of transketolase and their affinity towards the substrates (xylulose-5-phosphate and ribose-5-phosphate) has been studied in the presence of Ca2+ and Mg2+. In the presence of Ca2+, the active sites exhibit negative cooperativity in binding both xylulose-5-phosphate (donor substrate) and ribose-5-phosphate (acceptor substrate) and positive cooperativity in the catalytic transformation of the substrates. In the presence of Mg2+, nonequivalence of the active sites is not observed.
KEY WORDS: transketolase, nonequivalence of active sites, bivalent cations, xylulose-5-phosphate, ribose-5-phosphate