Enzyme and metabolite profiles of the pentose phosphate pathway in hypocotyls of Phaseolus mungo seedlings

Abstract

Activities of all the enzymes of the pentose phosphate (PP) pathway and amounts of all the intermediates of the pathway in three parts of hypocotyls of etiolated Phaseolus mungo seedlings, representing different stages of differentiation, were determined. The activities of the enzymes of the PP pathway were higher in the immature part, but the relative amounts of the enzymes were fairly constant in the different parts investigated. From the enzyme profile data, the rate-limiting enzymes of the pathway appear to be transketolase (TK), transaldolase (TA) and riboluse phosphate epimerase (RuPE). On the other hand, the data of steady-state concentrations of intermediates suggested that the glucose-6-phosphate dehydrogenase (G6PDH) step may participate in control. The regulation mechanisms of the PP pathway in the hypocotyl are also discussed.