Pentose phosphate pathway enzymes in nitrogen-fixing leguminous root nodules

Abstract

The enzymes glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, transketolase, transaldolase, d-ribose-5-phosphate ketol-isomerase, d-ribulose-5-phosphate 3-epimerase and dihydrofolate reductase were shown by sucrose density gradient centrifugation to be associated with the plastid and soluble fractions of soybean ( Glycine max) nodule extracts. These enzymes increased in specific activity during the development of the nodules. The specific activities of pentose phosphate pathway enzymes and dihydrofolate reductase were also measured in extracts of pea ( Pisum sativum), yellow lupin ( Lupinus luteus), broad bean ( Vicia faba), cowpea ( Vigna unguiculata), pigeon pea ( Cajanus cajan) and chick pea ( Cicer arietinum) nodules. With the exception of chick peas, the specific activities of the enzymes were greater in nodules that export fixed nitrogen predominantly as ureides than in those which are amide exporters.