the cytosolic ribose-5-phosphate isomerase catalyzes the reversible interconversion of ribulose-5-phosphate and ribose-5-phosphate in the non-oxidative phase of the oxidative pentose phosphate pathway
enzyme is involved in the first step of the non-oxidative branch of the pentose phosphate pathway. Two ribose 5-phosphate isomerase, RpiA and RpiB. RpiA is constitutively expressed, accounts for about 99% of the total ribose 5-phosphate isomerase activity for strains grown in nutrient broth. Escherichia coli strains defective in rpiA gene are still able to use ribose as a carbon source due to the presence of the second RPI, a ribose-inducible RpiB
CTRPI has a narrow substrate specificity for rare sugars and reversibly converts aldose substrates containing hydroxyl groups oriented in the same direction to one of the corresponding ketoses. CTRPI prefers aldose substrates such as L-talose, D-ribose and D-allose
enzyme displays activity only with aldose substrates possessing hydroxyl groups oriented in the right-handed configuration (Fischer projections) at the C2 and C3 positions, such as D-ribose, D-allose, L-talose, L-lyxose, D-gulose, and L-mannose. The specific activity decreases in the order D-ribose, D-allose, L-talose, L-lyxose, D-gulose, L-mannose
enzyme displays activity only with aldose substrates possessing hydroxyl groups oriented in the right-handed configuration (Fischer projections) at the C2 and C3 positions, such as D-ribose, D-allose, L-talose, L-lyxose, D-gulose, and L-mannose. The specific activity decreases in the order D-ribose, D-allose, L-talose, L-lyxose, D-gulose, L-mannose
ribose 5-phosphate isomerase and ribulose-5-phosphate kinase produce and utilize, respectively, a form of ribulose 5-phosphate which is not the predominant form in the aqueous solution. The effect of this specificity will be channelling of ribulose 5-phosphate from the isomerase to the kinase during photosynthesis
physical interaction between phosphoribulokinase and ribose-5-phosphate isomerase in the presence of substrate can facilitate direct transfer of ribulose 5-phosphate between the two enzymes
the constitutive ribosephosphate isomerase A catalyzes the formation of ribose 5-phosphate from ribulose 5-phosphate and also participates in the reverse reaction during ribose and adenosine catabolism. The normal physiological role of the inducible ribosephosphate isomerase B is still uncertain
the enzyme catalyzes the interconversion of D-ribose-5-phosphate and D-ribulose-5-phosphate in the reductive and oxidative pentose phosphate pathways and thus plays an important role in the primary metabolism of both photosynthetic and non-photosynthetic organisms