Arginine and Ornithine

At least seven different systems are known for transporting amino acids into cells. In the inherited disorder cystinuria, the carrier system responsible for reabsorption of the amino acids cysteine, ornithine, arginine, and lysine in the proximal convoluted tubule of the kidney is defective. The inability to reabsorb cystine leads to kidney stones. 

C. S5mthesis and Catabolism of Proline, Ornithine, Arginine, and Polyamines... 

A number of amino acid transport disorders may be associated with one or several of the systems described in Table 20.4. These are characterized by the excretion of amino acids in the urine but no increase in amino acid levels in the bloodstream. They are usually of hereditary origin. The most common disorder is cystinuria, characterized by the excretion of cystine. Because cystine is only slightly water soluble, cystinuria is often accompanied by the deposition of cystine-containing stones in the genitourinary tract. Cystinuria is apparently caused by a defect in the cationic amino acid transport system. Another disease that affects this system is lysinuric protein intolerance, which is associated with a failure to transport lysine, ornithine, arginine, and citrulline across membranes. Citrulline and ornithine are urea cycle intermediates (see later), and a disruption of their interorgan traffic results in hyperammonemia. 

Biosynthesis of Ornithine, Arginine, and Creatine Phosphate (Figure 2L2,... 

Cystinuria is an autosomal recessive disorder of renal mbular teab-sorption of cystine, ornithine, arginine and lysine (mnemonic COAL). Cystine (a dimer of cysteine Chapter 6) is sparingly soluble and accumulates in the tubular fluid, forming bladder and kidney stones (cystine urolithiasis). Cystine is so-called because cystine stones were discovered in the cyst (i.e. bladder). 

Transamination of glyoxalate takes place with several amino acid donors glycine, glutamate, ornithine, arginine, and methionine. 

In contrast, the renal clearance of cystine is 30 times greater in cystinurics than in normal individuals. Ornithine, arginine, and lysine are spilled in the urine along with cystine, and the renal clearance of these four amino acids is increased. 

As the preceding discussion shows, the Hterature which invokes the existence of an intermediate with C2v symmetry between ornithine/arginine and the tro-panes in Datura species commonly assumes that this intermediate is located on the pathway between the amino acids and M-methylpyrrolinium salt (10). From studies of the incorporation of more advanced precursors into tropine (1) to be discussed in detail below, it is becoming apparent that this assumption may not necessarily be warranted. 

The tropane alkaloids (TA), synthesized mainly in roots of several Solanaceous plants, are derived from ornithine, arginine and pheny-lanine [122, 210, 211]. A number of TAs, including atropine, hyoscyamine, scopolamine and the more active form, 6,7- 3-epoxide scopolamine, are used in medicine, primarily as anti-... 

An amino acid excreted in large amounts in the urine in the inborn error, cystinuria. This condition is due to a failure of the tubular reabsorption mechanism for the dibasic amino acids, cystine, ornithine, arginine and lysine. Two types of hyperlysinaemia... 

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