Berger M G, Sprengart M L, Kusnan M, Fock H P
Universität Kaiserslautern, Fachbereich Biologie, Postfach 3049, 6750 Kaiserslautern, Federal Republic of Germany.
Plant Physiol. 1986 Jun;81(2):356-60. doi: 10.1104/pp.81.2.356.
Succulent stems of Cissus quadrangularis L. (Vitaceae) contain glutamine synthetase, glutamate synthase, and glutamate dehydrogenase. The CO(2) and water gas exchanges of detached internodes were typical for Crassulacean acid metabolism plants. During three physiological phases, e.g. in the dark, in the early illumination period after stomata closure, and during the late light phase with the stomata wide open, (15)NH(4)Cl was injected into the central pith of stem sections. The kinetics of (15)N labeling in glutamate and glutamine suggested that glutamine synthetase was involved in the initial ammonia fixation. In the presence of methionine sulfoximine, an inhibitor of glutamine synthetase, the incorporation of (15)N derived from (15)NH(4)Cl was almost completely inhibited. Injections of amido-(15)N glutamine demonstrated a potential for (15)N transfer from the amido group of glutamine into glutamate which was suppressed by the glutamate synthase inhibitor, azaserine. The evidence indicates that glutamine synthetase and glutamate synthase could assimilate ammonia and cycle nitrogen during all phases of Crassulacean acid metabolism.
四角叶白粉藤（葡萄科）的肉质茎含有谷氨酰胺合成酶、谷氨酸合酶和谷氨酸脱氢酶。离体节间的二氧化碳和水汽交换是景天酸代谢植物的典型特征。在三个生理阶段，即在黑暗中、气孔关闭后的早期光照期以及气孔完全开放的后期光照阶段，将（15）氯化铵注入茎段的中央髓部。谷氨酸和谷氨酰胺中（15）N标记的动力学表明谷氨酰胺合成酶参与了最初的氨固定。在谷氨酰胺合成酶抑制剂甲硫氨酸亚砜亚胺存在的情况下，源自（15）氯化铵的（15）N掺入几乎被完全抑制。酰胺-（15）N谷氨酰胺的注射表明存在谷氨酰胺酰胺基团中的（15）N向谷氨酸转移的潜力，而这种转移被谷氨酸合酶抑制剂重氮丝氨酸所抑制。证据表明，谷氨酰胺合成酶和谷氨酸合酶可在景天酸代谢的所有阶段同化氨并循环氮。
