Nitrogen homeostasis

Grubinko, V.V. (1991). The role of glutamine in maintaining nitrogen homeostasis in fish (In Russian). Gydrobiologicheskii Zhumal 27,46-56. 

Within the liver, elimination of ammonia occurs via urea synthesis (Chapter 17). Since urea is uncharged, it does not disturb the acid-base balance. Many interorgan relationships in protein and nitrogen homeostasis arose because of the role that the liver plays in excess nitrogen excretion. 

Blood urea nitrogen (BUN) A waste product in the blood produced from the breakdown of dietary proteins. The kidneys filter blood to remove urea and maintain homeostasis. A decline in kidney function results in an increase in BUN. 

FRET-based nanosensors have been successfully used to monitor steady state levels of metabolites, nutrients, and ions in mammalian cells [74, 87], Recently FRET-based glucose, sucrose, and amino acid nanosensors have been developed to study the metabolism of glucose, sucrose, and amino acid uptake and metabolism in plant cells [80,89, 91]. The enormous potential of these nanosensors will be crucial for understanding ion (e.g., calcium), metabolite (e.g., sugars), hormone (e.g., auxins, gibberellins etc.), and nutrient (e.g., nitrogen, potassium, phosphorus) requirements and homeostasis in living plant tissues. 

The diet must provide those amino acids which the body cannot synthesize (essential amino acids, EAA) and nitrogen in the form of nonessential amino acids (NEA). Both EAA and NEA are required for biosynthesis of proteins and other nitrogen-containing compounds necessary for homeostasis or growth. Thus, the total nitrogen content of a specific food must be considered to be nutritionally significant. 

In the context of iron coordination by oxygen/nitrogen, the iron transport and storage proteins, transferrin and ferritin, which are the essential parts of iron homeostasis in cells, are also treated here. 

Homeostasis at the cellular and, especially, at the organismal level includes equilibrium between the formation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) and reactions of antioxidants maintaining appropriate levels of ROS and minimizing their unspecific reactions with vital biomolecules. Understanding this aspect of homeostasis is the reason for interest in antioxidant levels in the body and the antioxidant content of food and beverages. 

In both proposed feedback mechanisms, the dominant controUing factor is the surface ocean NO3 to PO ratio (see Fig. 1.16). Both feedbacks are expected to operate in situations of excess NO3 (i.e., high NOj to PO ratio, shown at the bottom of the feedback loop in Fig. 1.16), as well as in situations ofNO deficiency (i.e., low NO to PO ratio, shown at the top of the feedback loop), if this view is correct, these two feedbacks would provide a rather tight control of the marine nitrogen cycle, creating a well balanced homeostasis. A further consequence is that... 

Codispoti, L. A. (2006). An oceanic fixed nitrogen sink exceeding 400 Tg N a" vs the concept of homeostasis in the fixed-nitrogen inventory. Biogeosciences 3, 1203—1246. 

Hansinger, D. Organization of hepatic nitrogen metabolism and its relation to acid-base homeostasis. Khn. Wschr. 1990 68 1096-1101... 

Brain extracellular concentrations of amino acids and divalent metals (e.g., manganese) are primarily regulated by astrocytes. Adequate glutamate homeostasis is essential for the normal functioning of the central nervous system (CNS), for example, glutamate is important for nitrogen metabolism and, along with aspartate, is the primary mediator of the excitatory... 

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