ASPARTATE AND ALANINE MOVEMENT ACROSS SYMBIOTIC MEMBRANES OF SOYBEAN NODULES

Aspartate, alanine and glutamate uptake into bacteroids and symbiosome s isolated from soybean nodules were measured. An aspartate transport mechanism was identified in free bacteroids, with an apparent K-m of 2 7.5 mu M and a V-max of 5.14 nmol mg(-1) min(-1). Inhibitor studies in dicated that aspartate uptake was dependent on a proton motive force a cross the bacteroid membrane. Aspartate transport was competitively in hibited by glutamate with an apparent K-i of 9.7 mu M. Alanine uptake into bacteroids also showed saturation kinetics with a K-m of 12.2 mu M and V-max of 3.5 nmol mg(-1) min(-1). Bacteroids loaded with (14)Cas partate exchanged label for external cold aspartate, and glutamate. In contrast, there was no evidence for aspartate or alanine movement int o or out of intact symbiosomes except by slow passive diffusion. (C) 1 998 Elsevier Science Ltd. All rights reserved.