Kidney arginine synthesis

Urea cycle and arginine synthesis. The general aspect and control of the urea synthesis and the role of the intestine and kidney in arginine synthesis are shown above. 

Logically, ADH receptor antagonists, and ADH synthesis and release inhibitors can be effective aquaretics. ADH, 8-arginine vasopressin [113-79-17, is synthesized in the hypothalamus of the brain, and is transported through the supraopticohypophyseal tract to the posterior pituitary where it is stored. Upon sensing an increase of plasma osmolaUty by brain osmoreceptors or a decrease of blood volume or blood pressure detected by the baroreceptors and volume receptors, ADH is released into the blood circulation it activates vasopressin receptors in blood vessels to raise blood pressure, and vasopressin V2 receptors of the nephrons of the kidney to retain water and electrolytes to expand the blood volume. 

The synthesis of arginine from citrulline. The latter is produced from other amino acids in the small intestine and then released into the blood. The kidney takes up citrulline and converts it to arginine, which is then released into the blood for use by other tissues (Figure 8.18). Since arginine is a precursor for a number of important compounds, and aids wound healing, this is a significant biochemical role of the kidney. 

The synthesis of creatine. In the kidney, guanidinoace-tate is produced from arginine and glycine, then released into the blood to be taken up by the liver and methylated to form creatine (Figure 8.20(a)). The creatine is, in turn, taken up by the muscle where it is phosphorylated to produce phosphocreatine, which can maintain the ATP level, especially in explosive exercise. Creatine and phosphocreatine are converted in muscle to creatinine, which is important in clinical practice (Figure 8.20(b)) (Box 8.3). 

Figure 8.20 (a) The synthesis of phosphocreatine. The compound guanidinoacetate is formed from arginine and glycine in the kidney and is then transported to the liver where it is methylated addition of CHj (see Chapter 15) to form creatine (see Appendix 8.4 for details). Creatine is taken up by tissues/ organs/cells and phosphorylated to form phosphocreatine, particularly in muscle, (b) Conversion of phosphocreatine and creatine to creatinine in muscle. Creatinine is gradually formed and then released into blood and excreted in urine. 

The anorexia suffered by cancer patients is likely to arise from a combination of psychological stress, altered senses of taste and smell and increased levels of cytokines, which influence the appetite and satiety centres in the hypothalamus. There are several consequences micronutrient intake will be diminished and this may contribute to the signs and symptoms of the disease. Plasma amino acid levels will fall, as in starvation (Chapter 16). Synthesis of glutamine (by muscle, adipose and lung), aspartate (by liver), glutathione (by the intestine) and arginine (by the kidney) will all be compromised. The metabolic significance of all of these is discussed in Chapter 18. 

The final step of the urea cycle is the cleavage of arginine to release urea and regenerate ornithine. Ornithine then reenters the mitochondria via the ORNT-1 ornithine-citrulline antiporter. ARG-1 is a cytosolic homotrimeric enzyme of 35-kd monomers that is expressed in fiver and red blood cells. A second mitochondrial arginase (ARG-2) most likely plays a role in nitric oxide synthesis and is most abundant in brain, kidney, and prostate. ARG-1 deficiency is unique among the urea cycle deficiencies as patients do not present with hyperammonemia and encephalopathy but rather develop progressive spasticity of the lower limbs. Biochem-... 

Essential amino acids are indispensable in that the body is incapable of replacing them simply by using its own synthesizing facilities they must either be supplied in adequate quantities from outside or generated by degradation of body proteins. Non-essential amino acids are synthesized in the liver, muscles, kidneys and intestine. Only the synthesis of arginine from ornithine and the hydroxylation of phenylalanine to tyrosine are liver-specific reactions. 

Unlike fractions of pig-kidney protein, Neurospora crassa extracts can use L-glutamine, but not ammonium salts nor ammonium salts plus adeno-sine-5-triphosphoric acid. No synthesis of D-glucosamine is stimulated in Neurospora extracts by L-glutamic acid, L-aspartic acid, L-asparagine, L-alanine, glycine, L-valine, L-leucine, L-lysine, L-arginine, L-serine, L-cys-teine, L-citrulline, L-ornithine, butyramide, putrescine, or urea. Recently, a protein fraction has been discovered, in rat liver, that converts D-glucose... 

A. The amount of creatine in liver cells determines its rate of synthesis from glycine, arginine, and SAM. In muscle, creatine is converted to creatine phosphate, which is nonenzymati-cally cyclized to form creatinine. The amount of creatinine excreted by the kidneys each day depends on body muscle mass. In kidney failure, the excretion of creatinine into the urine will be low. 

F. 47.7. The synthesis of creatine from arginine, glycine, and S-adenosyl methionine. Synthesis originates in the kidney and is completed in the hver. 

Two different arginase (ARG) isoforms, with different biochemical characteristics and tissue distribution, have been identified (Reddi etal, 1975). These enzymes were shown to be the product of two different, but related genes (see Cederbaum et al, 2004). ARG I (liver type) is cytosolic and the last step of the urea cycle which regenerates ornithine and releases urea. In contrast, ARG II (kidney type) is present in the mitochondria and is involved in providing ornithine for poly amine and prohne synthesis (Cederbaum et al, 2004) and in regulating arginine availability for nitric oxide synthesis (Topal et al, 2006). ARG II is present in enterocytes and thus has the potential to generate ornithine... 

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