A lack of reactivity of d-arabinose 5-phosphate with enzymes of the pentose phosphate pathway

The reported conversion of d-arabinose 5-phosphate to d-ribose 5-phosphate and other intermediates of the pentose phosphate pathway was investigated. Two new solvent systems to separate the two aldopentose phosphates on paper and a method using chromatography on a column of dihydroxyboryl-cellulose were developed. No evidence for their interconversion could be obtained. d-Arabinose 5-phosphate did not serve as an acceptor for transketolase from bakers' yeast, Candida utilis, or rat liver but behaved as an inhibitor. d-Glucose 6-phosphate acted both as an acceptor and as an inhibitor of the reaction with d-ribose 5-phosphate as acceptor. d-Arabinose 5-phosphate was not converted into ribose 5-phosphate, ketopentose phosphate, triose phosphate, or a heptulose phosphate by rat muscle or rat liver enzymes. Hydroxypyruvate is suggested not to be a substrate for rat liver transketolase.