Pathways of Utilization of [1-14C] Glucose and [6-14C] Glucose in Slices of Peas

Abstract

Slices of ripening seeds of the pea (Pisum sativum) were supplied with [1-¹⁴C] G and [6-¹⁴C] G, and the S.A. was determined of the respirod carbon dioxide, pyruvate, and the acids of the T.C.A.C. as well as that of the individual carbon atoms of citrate and malate. The possibility that there exist active and inactive pools of the T.C.A.C. acids in the pea is considered and, for most of the acids, rejected. The results cannot be explained on the bais of the T.C.A.C. because the S.A. of the carbon dioxide liberated was some ten times higher than could have come from the malate via the T.C.A.C., too much ¹⁴C accumulated in the cycle acids to have come from pyruvate by the operation of the T.C.A.C., and the patterrn of label in citrate and malate was different from that expected. An alternative explanation is put forward based on the oxidation of glucose by the P.P.P. and movement of ¹⁴C by a series of rapid isotope exchange reactions.