Glucosidases (α,β) and trehalase (α) in the peribacteroid space and the bacteroid periplasm of Glycine max root nodules

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Components of the peribacteroid space (PBS) and the bacteroid periplasm (PPS) of soybean root nodules infected with Bradyrhizobium japonicum 61-A-101 were isolated by sucrose density gradient centrifugation. Non activity of either glucose-6 phosphate (glucose-6P)-dehydrogenase or alanine dehydrogenase, marker enzymes for the nodule and bacteroid cytoplasms, could be detected in the PBS and only minor activity of the bacteroid marker β-hydroxybutyrate dehydrogenase (0.06% of bacteroid activity). One dimensional SDS-PAGE of the PBS and the PPS revealed similar patterns for these two fractions. In the PBS fraction some proteins were quantitatively enhanced. The same enzyme activities were present in the PBS and the PPS but several enzymes had much higher specific activities in the PBS than in the PPS. The specific activities of α-glucosidase and α-trehalase in the PBS were 34-fold, 25-fold and 8-fold higher, respectively, than in the nodule cytoplsm. No activity was founds in root cytoplasm. The enzymes are considered as symbiosis specific proteins, enriched in the peribacteroid space. The estimated isoelectric point for α-glucosidase was 7.2 and for α-trehalase, 5.6 α-glucosidase and α-trehalase were not present in root cytoplasm. The possible functions of these PBS enzymes in symbiotic nitrogen fixation are discussed.