Incorporation of 15N2 into Various Fractions of Soybean Root Nodules

Abstract

Excised soybean root nodules exposed to an atmosphere containing an excess of 15N2 incorporated the label first into the centrifugal fraction containing the intracellular membrane envelopes and small amounts of bacteroid cell walls. The 15N con-centration then increased in the soluble portion of the nodules. The bacteroid fraction was not labelled after a 2 hour exposure of the nodules to 15N2. In ageing nodules incorporation of 15n into the soluble fraction declined before incorporation into the membrane fraction. The inhibitory effects of CO, N2O and H2 on 15N2 incorporation in the various fractions were studied; the results suggested differential inhibition. The membrane fraction contained 8.5% (w/v) total N, 37% (w/w) lipid, had a negligible O2 uptake in the presence of substrates and had an absorption spectrum suggestive of the presence of porphyrin compounds. Further fractionation of the membrane fraction indicated that the 15n was associated with the lighter particles and was only partially soluble in 3[image]-HCl. The possibility that the membrane fraction contained the site of primary N2 activation is discussed.