RESUMO
The effect of hexacyanoferrate(III) on the catalytic activity of transketolase has been studied. This oxidant inactivates only one of two active sites of the enzyme, the one with a higher affinity to the coenzyme (thiamine diphosphate). The second active site does not lose its catalytic activity. These observations indicate that the active sites of holotransketolase, being indiscernible by data of X-ray analysis, exhibit functional nonequivalence.
Assuntos
Ferricianetos/farmacologia , Transcetolase/antagonistas & inibidores , Catálise , Domínio Catalítico , Ferricianetos/química , Cinética , Tiamina Pirofosfato/química , Tiamina Pirofosfato/metabolismo , Transcetolase/química , Transcetolase/metabolismoRESUMO
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.