Enzymes of sucrose, maltose, and ?,?-trehalose catabolism in soybean root nodules

Abstract

Crude, Sephadex-filtered extracts of soybean (Glycine max (L.) Merr.) root nodules contained invertase (E.C. 3.2.1.26) activity with pH optima at 5.4 and 7.8, α,α-trehalase (E.C. 3.2.1.28) activity with pH optima at 3.8 and 6.6, and maltase (E.C. 3.2.1.20) activity with a broad pH optimum between 4.5 and 5.0. Bacteroids and cytosol were separated using Percoll density gradients. Cellulase and pectinase were employed to separate protoplasts from the infected region from the nodule cortex, which remained intract. Assays of disaccharidases from these nodule fractions indicated the following localization of enzymes: (1) Bacteroids lack invertase activity (pH 5.4 and 7.8). (2) Much, if not most, of the invertase activity may be localized in the nodule cortex; this is especially likely for acid invertase. However, there was substantial invertase activity in cytosol from the infected region. (3) Most of the maltase activity (pH 5.0) and trehalase activity (pH 3.8 and 6.6) were localized in the cytosol. It is likely that most of these disaccharidase activities are in the cytosol of the infected region, in contrast to invertase. (4) Bacteroids contain maltase (pH 5.0) and trehalase (pH 3.8 and 6.6), but the amount of these enzyme activities was less than 15% of total activity in nodules. Bacteroids and nodule cortex were capable of in-vivo hydrolysis of [(14)C]trehalose and [(14)C]maltose. These disaccharides were also hydrolyzed by soybean roots and hypocotyls. Therefore, while α,α-trehalose in soybean nodules is probably synthesized by the bacteroids, the capability for utilization of trehalose was not restricted to the bacteroids.