Purines degradation

Name changes may be confusing here when AMP loses the phosphate to become adenosine and adenosine loses the ribose to become adenine, it s still easy to tell who came from where. When IMP loses the phosphate, it becomes inosine, but when inosine loses the ribose it becomes hypoxanthine. It may be a little confusing, but it s still better than trying to pronounce inonine. 

---

The presence of uricase assists the uric acid to be hydrolysed, and the end product of purine degradation is completed with the addition of uricase. 

Purine Synthesis Purine Salvage Deoxynucleotides Purine Degradation... 

In an earlier report (J>), the decay of healthy yam tubers during storage was shown to be a result of catabolism of its proteins by an active a-glutamyl transpeptidase. There is also some alkaline proteolytic activity in the yam tuber (6), but little information is available on individual enzymes of the purine degradative pathway and on the properties of an alkaline proteinase that may function in yams during storage. This report describes the interrelation of five enzymes of ureide metabolism in fresh and stored yams, the release of ammonia in vitro by three of the enzymes that may provide an environment for alkaline proteinase activity in vivo, and the in vitro properties of an... 

This suggests that allantoinase may be the limiting enzyme in the purine degradative pathway. 

A 12-week-old infant with a history of persistent diarrhea and candidiasis is seen for a respiratory tract infection with Pneumocystis carinii. A chest x-ray confirms pneumonia and reveals absence of a thymic shadow. Trace IgG is present in his serum, but IgA and IgM are absent. His red blood cells completely lack an essential enzyme in purine degradation. The product normally formed by this enzyme is... 

Gout is one of the most ancient diseases its clinical characteristics have been known for at least 2000 years. It is now very effectively treated with drugs that decrease production of uric acid by inhibition of the enzyme xanthine oxidase in purine degradation (Figure 10.9) (allopurinol), and a drug that increases the excretion of uric acid (probenecid)... 

The fact that purine degradation in humans already stops at the uric acid stage can lead to problems, since—in contrast to allantoin—uric acid is poorly soluble in water. When large amounts of uric acid are formed or uric acid processing is disturbed, excessive concentrations of uric acid can develop in the blood hyperuricemia). This can result in the accumulation of uric acid crystals in the body. Deposition of these crystals in the joints can cause very painful attacks of gout. 

FIGURE 22-45 Catabolism of purine nucleotides. Note that primates as uric acid from purine degradation. Similarly, fish excrete much more... 

Hypoxanthine is oxidized by xanthine oxidase to xanthine, which is further oxidized by xanthine oxidase to uric acid, the final product of human purine degradation. Uric acid is excreted in the urine. 

Major pathways of purine degradation in animals. Primates excrete uric acid. Mammals other than primates catabolize uric acid to other end products. In contrast to the catabolism of carbohydrates, lipids, or... 

In addition to analyzing compounds, enzyme sensor has been used to determine the freshness of meats. Xanthine oxidase has been used to determine the levels of xanthine and hypoxanthine that are accumulated from purine degradation during muscle aging so as to monitor fish freshness for a long time. Traditional methods including the automated colorimetric method (54) were time consuming. Jahn et al (55) developed a dipstick test by... 

TAC of blood plasma in rats fed an ethanol-supplemented diet increases, although ethanol is known to induce oxidative stress. The effect is due to ethanol-induced purine degradation and increase in the level of uric acid (G2). TAC of blood plasma in critically ill patients with renal dysfunction is augmented, again due to increase in uric acid level (Ml). Caloric restriction, a procedure known to improve the redox status and prolong the life span of mammals, decreases TAC of rat serum (C12). 

Although both pyrimidines and purines are components in nucleic acids, they are made in different ways. Likewise, the products of pyrimidine degradation are more water-soluble than are the products of purine degradation. 

Allopurinol is a drug given to gout sufferers. It inhibits an enzyme of the purine degradation pathway called xanthine oxidase by acting in the capacity of a substrate. However, its product, oxidized allopurinol, is not able to leave the active site of the enzyme, thus blocking it. Is there a name for this type of substrate What inhibition kinetics would you observe with a Lineweaver-Burk plot, and why ... 

A very important enzyme is xanthine oxidase, which catalyzes two reactions in the purine degradation process. It contains a number of subunits, and Fe, Mo, and FAD are its prosthetic groups. It acts, in this case, as an oxidase using 02 as an electron sink. In other reactions, however, this enzyme can act as a dehydrogenase using NAD+ as an oxidizing agent. A xanthine oxidase... 

Only in certain animals is uric acid further degraded, and it is a purine degradation product, not a pyrimidine. 

---