Schultz N A, Benson D R
Department of Molecular and Cell Biology, University of Connecticut, Storrs 06269-3044.
J Bacteriol. 1990 Mar;172(3):1380-4. doi: 10.1128/jb.172.3.1380-1384.1990.
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.
弗兰克氏菌属是一类丝状放线菌，可在培养基以及放线菌根瘤中固定氮气。在有氧且缺乏化合态氮的环境中，固氮酶局限于厚壁球状结构，即弗兰克氏菌泡囊，这些泡囊沿着营养菌丝的短柄形成。测定了在以铵根离子和氮气为氮源生长的细胞中，以及在通过蔗糖梯度分离的固氮培养物的泡囊和菌丝中，铵根离子同化酶（谷氨酰胺合成酶[GS]、谷氨酸合酶、谷氨酸脱氢酶和丙氨酸脱氢酶）的活性。通过酶活性测定和二维聚丙烯酰胺凝胶电泳表明，两种弗兰克氏菌谷氨酰胺合成酶GSI和GSII在泡囊中的含量与在固氮培养物的营养菌丝中检测到的含量相似。谷氨酸合酶、谷氨酸脱氢酶和丙氨酸脱氢酶的活性局限于营养菌丝。泡囊显然缺乏在谷氨酰胺阶段之后同化氨的完整途径。
