The isocitrate dehydrogenase (L,-isocitrate: NADP oxidoreductase, decarboxylating, EC 1.1.1.42) catalyses, in the presence of TPN, the oxidative decarboxylation of isocitrate to a-ketoglutarate and CO,. The enzyme catalyses also a tritium exchange reaction between tritiated a-ketoglutarate and water; this reaction requires the presence of 1,4 TPNH [l] , but the role of the reduced coenzyme in this reaction is unknown. Alsot the tritium exchange reaction, catalysed by 6- phosphogluconate dehydrogenase, between tritiated ribulose Sphosphate and water, requires the presence of I,4 TPNH [2] . In this case there are indications that the nitrogen of the nicotinamide ring of the reduced coenzyme influences the ionization of amino acid residues involved in both the tritium exchange reaction and in the binding of the coenzyme to the enzyme [3,4] . In the present paper we report some experiments which indicate that also in the case of isocitrate dehydrogenase the pyridine nitrogen of the reduced coenzyme seems to play a role in the tritium exchange reaction.
A role for the pyridine nitrogen of reduced triphosphopyridine-nucleotide in the mechanism of action of isocitrate dehydrogenase
RIPPA, Mario;SIGNORINI, Marco;DALLOCCHIO, Franco Pasquale Filippo
1974
Abstract
The isocitrate dehydrogenase (L,-isocitrate: NADP oxidoreductase, decarboxylating, EC 1.1.1.42) catalyses, in the presence of TPN, the oxidative decarboxylation of isocitrate to a-ketoglutarate and CO,. The enzyme catalyses also a tritium exchange reaction between tritiated a-ketoglutarate and water; this reaction requires the presence of 1,4 TPNH [l] , but the role of the reduced coenzyme in this reaction is unknown. Alsot the tritium exchange reaction, catalysed by 6- phosphogluconate dehydrogenase, between tritiated ribulose Sphosphate and water, requires the presence of I,4 TPNH [2] . In this case there are indications that the nitrogen of the nicotinamide ring of the reduced coenzyme influences the ionization of amino acid residues involved in both the tritium exchange reaction and in the binding of the coenzyme to the enzyme [3,4] . In the present paper we report some experiments which indicate that also in the case of isocitrate dehydrogenase the pyridine nitrogen of the reduced coenzyme seems to play a role in the tritium exchange reaction.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
