Purification and characterization of a specific nucleoside diphosphatase from soybean root nodules

A specific nucleoside diphosphatase was purified from the plant portion of soybean (Glycine max L.) root nodules. This enzyme is highly specific for nucleotide diphosphates; it is unable to hydrolyze nucleotide tri- and monophosphates or a variety of other phosphorylated compounds. It will, however, hydrolyze any nucleotide disphosphate tested. The pH optimum of the enzyme is about 7.5; it requires a divalent cation for activity; and it is neither inhibited nor activated by any of the metabolites tested. It appears that in vivo this enzyme would be very active, but its function is not clear.     

Affinity purification and some properties of nucleoside diphosphatase from rat liver cytosol.

Nucleosidediphosphatase (nucleosidediphosphate phosphohydrolase, EC 3.6.1.6) of rat liver cytosol was purified up to 336--fold by the procedure including affinity chromatographies of concanavalin A- and alanine-Sepharose. The final purified enzyme showed a single protein band upon polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Its native form was found to be a tetramer with molecular weight of 120 000 which consists of subunit with molecular weight of 30 000. The enzyme was found to be a glycoprotein on the basis of its chromatographic behaviour with concanavalin A-Sepharose and positive staining with periodate-Schiff reaction in polyacrylamide gels. Furthermore, the two molecular forms with isoelectric points of 4.7 and 5.0 were demonstrated by electrofocusing, though they did not show any significant difference with respect to their catalytic properties.     

Thiamine pyrophosphatase (nucleoside diphosphatase) in the Golgi apparatus is distinct from microsomal nucleoside diphosphatase

The properties of thiamine pyrophosphatase in the Golgi apparatus of rat liver were studied. Thiamine pyrophosphatase in an extract of the Golgi apparatus was separated into 6 bands of between pH 5.4 and 6.3 by isoelectric focusing on polyacrylamide gel. On the gels all these subforms catalyzed the hydrolyses of GDP, IDP, UDP, and CDP as well as that of thiamine pyrophosphate. The characteristics resembled those of Type B nucleoside diphosphatase of rat brain, though the enzyme did not have 3 subforms of Type B nucleoside diphosphatase in the higher pH region on isoelectric focusing. Thiamine pyrophosphatase of the Golgi apparatus was separated from microsomal nucleoside diphosphatase by DEAE-cellulose column chromatography. The properties of the enzyme were quite similar to those of Type B nucleoside diphosphatase with respect to its substrate specificity, optimum pH for activity, and inhibition by ATP. These findings suggest that thiamine pyrophosphatase in the Golgi apparatus is different from microsomal nucleoside diphosphatase and that it might be basically the same enzyme as Type B nucleoside diphosphatase except for different extents of modification.     

Estimation of ammonium concentration in the cytosol of soybean nodules

Analysis of ammonium concentration in the cytosol of soybean (Glycine max [L.] Merr.) root nodules gave high levels of error variation. When the separation of cytosol and bacteroids was deliberately delayed following nodule maceration, a large increase in ammonium concentration was found in the cytosol. When a series of samples was subjected to delay intervals of 0 to 60 minutes, extrapolation of the regression line to time zero indicated that the ammonium concentration in cytosol at the time of nodule maceration was essentially nil. The source of ammonium buildup following maceration was not found, but hydrolysis of free amino acids or ureides was ruled out. An extremely low concentration of ammonium in the cytosol is consistent with a model for movement of ammonia (or ammonium) from bacteroids to host cytoplasm by diffusion.     

Nucleoside diphosphatase and 5'-nucleotidase activities of soybean root nodules and other tissues

Nucleoside diphosphatase and 5′-nucleotidase activities were both found to be very high in extracts of soybean (Glycine max L.) root nodules. Both activities increased early in soybean nodule development, prior to the rise in leghemoglobin, and both were found at equivalent levels in nitrogenfixing and nonfixing nodules. Based on a survey of other tissues, these activities were both highest in soybean nodules (1300 nanomoles per milligram protein per minute, nucleoside diphosphatase and 500 nanomoles per milligram protein per minute, 5′-nucleotidase), but they were not always associated with each other; in some tissues one was high and the other low. Neither activity correlated well with ureide production; both seem, rather, to be primarily involved in some other metabolic function. Both the nucleoside diphosphatase and 5′-nucleotidase of soybean nodules were soluble proteins, and neither appeared to be associated with plastids, mitochondria, or bacteroids.     

Carbohydrate, organic Acid, and amino Acid composition of bacteroids and cytosol from soybean nodules

Metabolites in Bradyrhizobium japonicum bacteroids and in Glycine max (L.) Merr. cytosol from root nodules were analyzed using an isolation technique which makes it possible to estimate and correct for changes in concentration which may occur during bacteroid isolation. Bacteroid and cytosol extracts were fractionated on ion-exchange columns and were analyzed for carbohydrate composition using gas-liquid chromatography and for organic acid and amino acid composition using high performance liquid chromatography. Analysis of organic acids in plant tissues as the phenacyl derivatives is reported for the first time and this approach revealed the presence of several unknown organic acids in nodules. The time required for separation of bacteroids and cytosol was varied, and significant change in concentration of individual compounds during the separation of the two fractions was estimated by calculating the regression of concentration on time. When a statistically significant slope was found, the true concentration was estimated by extrapolating the regression line to time zero. Of 78 concentration estimates made, there was a statistically significant (5% level) change in concentration during sample preparation for only five metabolites: glucose, sucrose, and succinate in the cytosol and d-pinitol and serine in bacteroids. On a mass basis, the major compounds in bacteroids were (descending order of concentration): myo-inositol, d-chiro-inositol, alpha,alpha-trehalose, sucrose, aspartate, glutamate, d-pinitol, arginine, malonate, and glucose. On a proportional basis (concentration in bacteroid as percent of concentration in bacteroid + cytosol fractions), the major compounds were: alpha-aminoadipate (94), trehalose (66), lysine (58), and arginine (46). The results indicate that metabolite concentrations in bacteroids can be reliably determined.     

Thiamine pyrophosphatase and nucleoside diphosphatase in rat brain

Two types of nucleoside diphosphatase were found in rat brain. One (Type L) had similar properties to those of the liver microsomal enzyme with respect to its isoelectric point, substrate specificity, Km values, optimum pH, activation by ATP and molecular weight. The other (Type B), which separated into multiple forms on isoelectric focusing, had lower Km values and a smaller molecular weight than the Type L enzyme, and was inhibited by ATP. The Type B enzyme catalyzed the hydrolysis of thiamine pyrophosphate as well as those of various nucleoside diphosphates at physiological pH, while Type L showed only nucleoside diphosphatase activity at neutral pH. These findings suggest that the two enzymes play different physiological roles in the brain.     

Nodule-specific polypeptides from effective alfalfa root nodules and from ineffective nodules lacking nitrogenase

In addition to leghemoglobin, at least nine nodule-specific polypeptides from the alfalfa (Medicago sativa L.)-Rhizobium meliloti symbiosis were identified by immune assay. Some of these polypeptides may be subunits of larger proteins but none appeared to be subunits of the same multimeric protein. All nine of the nodule-specific polypeptides were localized to within the plant cytosol; they were not found in extracts of bacteroids or in the peribacteroid space. At least one of these nodule-specific polypeptides was found to be antigenically related to nodule-specific polypeptides in pea and/or soybean. Ineffective nodules elicited by R. meliloti strains containing mutations in four different genes required for nitrogenase synthesis contained reduced concentrations of leghemoglobin and of several of the nodule-specific polypeptides. Other nodule-specific polypeptides were unaltered or actually enriched in the ineffective nodules. Many of the differences between the ineffective and effective nodules were apparent in nodules harvested shortly after the nodules became visible. These differences were greatly amplified in older nodules. When the four ineffective nodule types were compared to one another, there were clear quantitative differences in the concentrations of several of the nodule-specific polypeptides. These differences suggest that lack of a functional nitrogenase does not have a single direct effect on nodule development.     

Localization of nucleoside diphosphatase in the onion root tip

Summary Nucleoside diphosphatase activity occurs in the Golgi apparatus, on the plasmalemma, between the plasmalemma and the definitive cell wall, and in the endoplasmic reticulum of the onion root tip. The presence and/or relative concentrations of reaction product at each of these cellular sites occur in distinctive developmental patterns within the root. Cells with high NDPase activity at any combination of these sites also produce large amounts of a polysaccharide-rich product. A vacuolar activity also occurs in the pericycle and cortex in a developmentally distinctive pattern, but its location has not been correlated to polysaccharide secretory activity.     

Properties of pyruvate kinase from soybean nodule cytosol

The properties of pyruvate kinase from soybean (Glycine max L.) nodule cytosol were examined to determine what influence the N₂ fixation process might have on this supposed key control enzyme. A crude enzyme preparation was prepared by chromatography of cytosol extract on a diethylaminoethyl-cellulose column. ATP and citrate at 5 mm concentrations inhibited pyruvate kinase 27 and 34%, respectively. Enzyme activation was hyperbolic with respect to both K⁺ and NH₄⁺ concentrations. In the presence of physiological concentrations of K⁺ and high phosphoenolpyruvate (PEP) concentrations, NH₄⁺ inhibited enzyme activity. Comparisons of kinetic parameters (V_max and apparent K_a) for NH₄⁺ and K⁺ with inhibition curves indicated that inhibition was very likely a result of competition of the ions for activation site(s) on the pyruvate kinase. In addition, apparent K_a (monovalent cation) and K_m (PEP) were influenced by PEP and monovalent cation concentrations, respectively. This effect may reflect a fundamental difference between plant and animal pyruvate kinases. It is concluded that control of cytosol pyruvate kinase may be closely related to reactions involved in the assimilation of NH₄⁺.     

Aldrin epoxidase from soybean root nodules

Soybean (Glycine max cv Forrest) root nodule homogenates oxidized aldrin to its epoxide, dieldrin. In crude tissue brei, addition of an NADPH-generating system was inhibitory to epoxidation. However, anaerobic gel filtration and sucrose density separation removed factors required for inhibition by NADPH, allowing a normal stimulation by the NADPH-generating system. In fractions from sucrose density gradients, activity was found predominantly at a density containing rough microsomes, with additional activities in the soluble and other fractions. Epoxidase activity was 2–4-times greater in the nitrogen-fixing nodules than in roots. This demonstration of active epoxidation indicates the capacity of nodules to detoxify other pesticides and xenobiotics.     

Comparisons of plasma membrane polypeptides from soybean and alfalfa

Polypeptides were solubilized with sodium dodecyl sulfate from plasma membrane vesicles of eight varieties of soybean roots [Glycine max (L.) Merr.] and of cultured alfalfa cells (Medicago sativa L.). The solubilized polypeptides were analysed by 2D-polyacrylamide gel electrophoresis. Apparent isoelectric point and MW values were obtained for 80 soybean plasma membrane polypeptides and 44 alfalfa plasma membrane polypeptides. From these data composite distribution patterns were constructed, which are representative of the soybean or alfalfa 2D-gels, respectively. The results showed that the general polypeptide staining patterns were similar for all the soybean varieties, but some minor differences were evident. The alfalfa electrophoretograms differed markedly from the soybean electrophoretograms in specific details, though some general pattern similarities were noted. The data are discussed in terms of a physiological role for the integral plasma membrane polypeptides and in terms of the potential for distinguishing among soybean varieties and between species at the plasma membrane polypeptide level.     

Leghaemoglobin biosynthesis in a new single cell system from soybean root nodules

Single cells were effectively released from 35–45-day-old soybean ( Glycine max L. cv. Yaefusanari) nodules by treatment with an enzymic solution containing 1 mg/ml maceration enzyme (Pectolyase Y-23), 0.5 M mannitol, 2% (w/v) sucrose and 0.5% (w/v) potassium dextran sulfate. Bacteroid-containing cells were purified by Percoll density gradient centrifugation. Electron microscopic observation showed that these cells were protoplasts enclosed by a thin wall and with well preserved internal structures including bacteroids. The single cells obtained were stable against centrifugation and vigorous pipetting. The cells retained the ability to synthesize proteins including leghaemoglobin. The ratio of leghaemoglobin components synthesized in the single cells was similar to that of components synthesized in the nodules. The bacteroidal cell fraction was further separated into three fractions by a Percoll density gradient centrifugation. Comparison of the absolute and relative leghaemoglobin content, the activity of glutamine synthetase in the cytoplasm and the activity of 3-hydroxybutyrate dehydrogenase in the bacteroid suggests that these fractions contained cells in different stages of symbiosis. This new single cell system should provide a useful experimental system for analyzing events in the root nodule.     

Purification and characterization of nucleoside diphosphatase from rat-liver microsomes. Evidence for metalloenzyme and glycoprotein

Nucleoside diphosphatase was purified from rat liver microsomes more than 3000-fold with a 16% yield using a procedure including concanavalin-A--Sepharose and phenyl-Sepharose column chromatography. The purified enzyme had a specific activity of 2500 units/mg protein and appeared homogeneous by gel electrophoresis. The enzyme had a sedimentation coefficient of 6.5 S by sucrose-density gradient centrifugation. The enzyme had a sedimentation coefficient of 6.5 S by sucrose-density gradient centrifugation, and a Stokes' radius of 4.8 nm was estimated by the gel filtration technique. Its molecular weight is 130,000, but only one single band of Mr 65,000 was detected after sodium dodecyl sulfate/polyacrylamide gel electrophoresis. The native enzyme seems thus to be composed of two identical subunits. The purified enzyme was confirmed to be a glycoprotein containing approximately 9% carbohydrates. The enzyme had a pH optimum of 7.5, an isoelectric point of 4.85 and a Km of 2.5 mM for UDP. On the basis of direct measurement of metal content in the native enzyme, the rat liver nucleoside diphosphatase was found to be a metalloenzyme containing 0.9 mol zinc and 0.1 mol manganese/mol 65,000-Mr subunit. Metal-free nucleoside diphosphatase has been prepared. The activity of the metal-free enzyme was restored by the addition of several divalent cations, zinc being the most effective.