title: Enzymes of ammonia assimilation in hyphae and vesicles of Frankia sp. strain CpI1.
abstract: Frankia spp. are filamentous actinomycetes that fix N2 in culture and in actinorhizal root nodules. In combined nitrogen-depleted aerobic environments, nitrogenase is restricted to thick-walled spherical structures, Frankia vesicles, that are formed on short stalks along the vegetative hyphae. The activities of the NH4(+)-assimilating enzymes (glutamine synthetase [GS], glutamate synthase, glutamate dehydrogenase, and alanine dehydrogenase) were determined in cells grown on NH4+ and N2 and in vesicles and hyphae from N2-fixing cultures separated on sucrose gradients. The two frankial GSs, GSI and GSII, were present in vesicles at levels similar to those detected in vegetative hyphae from N2-fixing cultures as shown by enzyme assay and two-dimensional polyacrylamide gel electrophoresis. Glutamate synthase, glutamate dehydrogenase, and alanine dehydrogenase activities were restricted to the vegetative hyphae. Vesicles apparently lack a complete pathway for assimilating ammonia beyond the glutamine stage.
authors.affiliation: Department of Molecular and Cell Biology, University of Connecticut, Storrs 06269-3044.
authors.forename: N A
authors.initials: NA
authors.lastname: Schultz
authors.forename: D R
authors.initials: DR
authors.lastname: Benson
mesh_terms: D000192:Actinomycetales / Q000201:enzymology* / Q000648:ultrastructure; D050788:Alanine Dehydrogenase; D000594:Amino Acid Oxidoreductases / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism*; D002458:Cell Fractionation; D002499:Centrifugation, Density Gradient; D005969:Glutamate Dehydrogenase / Q000378:metabolism; D005970:Glutamate Synthase / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics
chemical_list: D007527:Isoenzymes; D000641:Ammonia; D000594:Amino Acid Oxidoreductases; D050788:Alanine Dehydrogenase; D005970:Glutamate Synthase; D005969:Glutamate Dehydrogenase; D005974:Glutamate-Ammonia Ligase