Periplasmic metabolism of glutamate and aspartate by intact Bradyrhizobium japonicum bacteriods

• Published in: Biochimica et biophysica acta. General subjects Vol. 1035; no. 3; pp. 257 - 265
• Main Authors: Streeter, John G., Salminen, Seppo O.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 14.09.1990
• Subjects: Aspartate aminotransferase; Bacterial nutrition; Periplasmic enzyme; α-Ketoglutarate; Aspartate aminotransferase; α-Ketoglutarate; Bacterial nutrition; Periplasmic enzyme
• ISSN: 0304-4165; 1872-8006
• DOI: 10.1016/0304-4165(90)90087-D

In studies on the uptake and metabolism of [ 14C]glutamate by Bradyrhizobium japonicum bacteroids we found that, in the presence of unlabeled malate, succinate or α-ketoglutarate, substantial label was recovered in α-ketoglutarate in the reaction mixtures. As much as 30% of the total 14C supplied could be found in α-ketoglutarate in the reaction mixtures after 30 min and this occured in the absence of detectable labeling of α-ketoglutarate in the cells. The labeling of α-ketoglutarate was almost completely inhibited by aminooxyacetate (aminotransferase inhibitor). Direct assay of aspartate aminotransferase in intact bacteroids was possible in the presence of very dilute Tritron X-100 (≤ 0.02%, w/v). The response of the aminotransferase to detergent was similar to the response of phosphodiesterase, a periplasmic marker, and different from malate dehydrogenase and β-hydroxybutyrate dehydrogenase, cytoplasmic markers. Comparison of maximum enzyme activity assayable with intact bacteroids and maximum activity in sonicated bacteroids indicated that about half of the total cellular aminotransferase activity was accessible to the external medium. The combined labeling and enzyme assay results indicated that B. japonicum bacteroids have a capability for transamination in the periplasmic space. Although this may not be important in the transfer of reducing equivalents from host cytoplasm to bacteroids in nodules, the transamination capability may facilitate the acquisition of metabolites by free-living bacteria.